So what the heck is a Johnson Tee?
Most people are probably familiar with the air gap device that is present at the kitchen sink that prevents drainage water from flowing back into the dishwasher (nice thought). When they are plumbed backwards they make nice little fountains into the sink.
There is another method of venting the dishwasher that, while a little less common, does the same thing—-the “Johnson Tee.” These devices have been around for quite a while—-at least the early 1980’s when I was building houses in the Oswego, NY area. With this method of venting you won’t find the washer drain connected to the disposal or drain under the kitchen sink the way it would be with the countertop air gap. It leaves a much cleaner look and doesn’t use up the extra hole in the sink—which can then be used for something else—like a soap dispenser, a hot water tap or a push button vacuum switch for the disposal—or even a filtered water faucet.
With the Johnson Tee, the drain and washer connections are all behind the dishwasher and inside the wall cavity. The actual vent portion is at the exterior of the home (although sometimes it might be found on the countertop backsplash). This is what the assembly looks like inside the wall before the wall is closed in. At the very bottom of the picture you can see where the drain from the washer will connect.
At the top is where the Tee portion goes through the wall to the exterior and will have a finish cap installed that looks like the one in this next picture.
Like the countertop type air gap device, if you see water or foam coming out of the cap it is an indication of problems with the dishwasher drain and a plumber should be called to make repairs. The biggest problem that the Johnson Tee encounters is that the holes at the exterior get painted over—-which prevents proper function—-so the holes must be maintained open. Another thing that is common is that the test caps get left in place and never properly finished.
This can be remedied by simply drilling a few small holes in the cap or by cutting the cap off and installing the more decorative type pictured above.
So make sure your house is wearing its Johnson Tee or countertop air gap device properly.
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Charles Buell, Seattle Home Inspector
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Charles,
I just talked to Bosch and they tell me that Johnson Tee’s are not approved connections to the Bosch D/W. They also tell me that no other D/W is approved with it either. Do you know of any that will work with a Johnson Tee?
They do not like the additional length of the drain line or the fact that it is reduced to 1/2″ drain lines.
The smaller pumps are quieter but less effective.
Since most homes have johnson Tee’s, I guess I need to find a D/W compatible with them. Do you know of any?
Mark, this is very interesting. As it turns out, many newer dishwashers may not allow the Johnson-tees due to the 1/2″ drain size. I am suspect we may see some changes in the J-tee’s or they will likely disappear all together. I will have to check out some of the other manufacturer’s drain size requirements. Things are never static in this business 🙂 Of course if you already have a J-tee, you could always abandon it and put a countertop unit in. I will see what additional info I can find since these things make for a much nicer way of venting the washer.
Mark, I easily found installation instructions for Whirlpool, Amana and Kitchenaid that all call for a minimum of 1/2″ id drains—there are likely others as well
Why do the ‘Tees use only a 1/2″ line? Is there something inherent in the design that requires that?
The hose that came with our Bosch is only about 1/2″ and the hose end has a connector for 1/2″ so unless there’s some kind of fluid mechanics at work it seems a 1/2″ drain would be fine…
Just looked at the installation instructions on our 2011 Bosch and it doesn’t say anything about minimum drain size.
Steve, the drain inlet side of the Johnson Tee only comes in 1/2″—so if you have a dishwasher that requires a minimum size drain that is larger, you likely “technically” should not use the Johnson Tee. If your drain hose is 1/2″ I would think you would be fine using the Tee–but follow the manufacturer’s instructions or call them.
I am redoing the kitchen in a house we bought recently. We found the Johnson tee capped in the wall, not being used anymore. The dw was draining straight to the disposal. There is evidence that at some point, there was water damage behind the dw. I’m guessing the J-tee was abandoned for whatever reason that brought on the damage, possibly too small or long of a drain pipe? Blockage? Who knows.
Anyway, I read in some forum somewhere that someone had installed a y connection between the j-tee, the dw drain, and the garbage disposal, so that the dw still drains to the disposal, but also has the j-tee still connected. Do you have any thoughts on this? Is this okay? I’m thinking it might help with the size issue of the 1/2″ copper pipe being too small or getting clogged.
Thanks for your help!
I had a house with a Johnson Tee several years ago. Sure beats having that fountain on the counter top. I would like to install one in a house I am working on but I’m not sure where or how to tie ino the drain. I have a 1-1/2″ horisontal trap arm that runs from the sink, behind the dishwasher and around the corner to the drain/wet vent. Can I install a T-Wye in the trap arm with a P trap above it?
Al, I can’t quite visualize what you are asking—so you will need to ask a plumber I guess. Keep in mind that some of the newer dishwashers require a 5/8″ minimum ID drain line and the J-Tee is only 1/2″
Where may I buy a Johnson Tee?
Thank you.
J. A. Mendiguren
Jorge, you don’t say where you are located but they are certainly available in any “real” plumbing supply house in Washington State—and likely most any state that follows the UPC.
I have been experiencing dirty water going back into my dishwasher at the end of every cycle. I’ve discovered it has been installed with a Johnson tee. The outside vent is not blocked, but it is 6 feet away from the sink side edge of the dishwasher. And the drain hose is visible under sink until it goes into wall. I don’t know the hose diameter, it is plastic and corrugated, entering and exiting under sink cabinet at base level, but with lots of slack resulting in about a 12 inch high loop. I can send picture if it can help you, help me. Can’t figure how to attach it here. I can’t find any resources to verify if the Johnson Tee and corresponding visible setup is installed correctly to explain why it is not working and fix it.
Thank you
Joelle, well it sounds like something is wrong for sure—but you already know that 🙂 Could be a blockage on the way to the air gap—something that has maybe altered since originally installed (as the washer sounds like it is a long way from the air gap). Some of the newer washers require a drain bigger than the 1/2″ Johnson Tee—check washer installation instructions. If it has been working fine but is not now then I would look to some sort of blockage in the drain line. A plumber should be able to figure it out. But, sure, go ahead and send me pictures if you like.
Thank you, I have sent you an email.
A Johnson Tee is not an air gap. An air gap physically separates the sewage line from the supply line. A Johnson Tee has a vent such that a siphon should not occur: your dishwasher would suck air from outside, instead of pulling sewage.
If your sewage drains slowly or backs up, it can fill faster than the vent drains. In the event of a power loss in the water and sewage infrastructure, for example, the pumps in sewage stop, and human feces and water discharge (from flushing toilets) isn’t pumped along any uphill portion of sewage run. This moves backwards into buildings. With the failure in water supply, a loss of pressure in the water system can create a siphon effect, as water pulls downhill.
With an air gap, the sewage line overflows, and then spills out. It can’t reach the drain line at the dishwasher (due to the air gap). With the pressure running backwards, the siphon in your dishwasher sucks air.
Without an air gap, sewage back flow faster than your vent drains (or with a clogged vent) enters the dishwasher drain line. A siphon effect will suck sewage into the water mains system—at the street, outside—and subsequently introduce human feces into the drinking water system at large. Not your house, but every house.
If the siphon is sufficiently powerful, it can fill your dishwasher, and then back flow into the mains. In a washing machine, the fill valve is way up high, and there’s an open air valve above the water level (even in front-loaders); the washing machine is plugged into a standpipe, and so pressurized sewage doesn’t force its way back into the hose without siphon—which can’t happen due to the air gap inside the washing machine itself.
A double check valve configuration works as an effective back flow prevention device; however, a double check valve may fail at any time, and requires routine inspection and testing. An air gap can’t fail. The common high loop is an effective siphon and will draw sewage into the machine in these scenarios.
hello, in the article you mention that the Johnson Tee has a UPC listing. Can you tell me who the manufacturer or company name? There isn’t a listing with IAPMO R&T for this product under the name “Johnson Tee”
Albert Lee installed our Miele dishwasher and refused to connect the drain to the existing dishwasher drain (1/2″ Johnson Tee) installed 22 years ago when the house was built. Instead they connected it to the disposal, which is 1/2 inch also. OEM Manual says the drain cannot be higher than 1 Meter (39 inches). The dishwasher comes with a 7/8″ drain hose.
Tired of the sloshing water noise in the disposal, I re-plumbed the copper coming out of the top to 3/4″ and connected the dishwasher to it.
If they did not like the 1/2″ of the original drain, why would they be happy with a 1/2″ drain to the disposal? (Rhetorical question)
Hi Dan. How is this working with the 3/4″ copper? I’m in the situation. The wall is about to be closed up, but I can redo it with 3/4 copper.
Hello,
I have one of these type air gaps in my condo. I have one with a “decorative” finish cap as you mentioned above. It’s pulling away from the wall a little bit so there is a bit of a hole between the wall and the trim piece/pipe. Ants have decided to take advantage of this. Do you know if it would be okay to caulk between the wall and the trim so there is no hole for the ants to come through??
I would simply have a new cap installed. You might try just pushing this one in so that it is flush again, but I have to worn you it may disintegrate if it is older. Caulking the gap may work if it is not too big.
I’m trying to help my folks find a replacement decorative exterior cap (theirs is deteriorating due to being on the side of the house that gets with a lot of sun). Any recommendations as to where to find one?
Around here you can get them from Home Depot or any plumbing supply store.
We’re in Seattle and can’t seem to find the caps anywhere, even at HD. I took the remains of the cap part in to a HD and they didn’t even know want it was (even after explaining to them what it was). I can find the tee vent part online thru HD but no where can I find the cap. Any suggestions? I’d like to be able to cover the hole on the outside of my folks house 🙂
I bought one a month ago at the Bitterlake Home Depot and I know Morgans and Aurora plumbing have them.
Hey Charles,
I forgot to come back and say THANK YOU for the leads. We went to Aurora (we’re closer to them than Morgans) and they had them in stock and they were about $8 and change. We bought two just to have a spare on hand for the inevitable next replacement ;).
We found the replacement Johnson Tee exterior caps at Ferguson Plumbing in Auburn. I think we paid about $5.50.
I’m working on a house in escrow right now that had water damage from no flashing around the deck to house intersection. When I open a bay window area against a kitchen sink wall I found a Johnson Tee that didn’t terminate to the outside wall. I’m assuming the Tee should be extended to the outside.
Since the buyer’s inspection was stopped before they got inside due to outside water damage I’m wondering how Johnson Tees are view in general in the state of Washington.
Would you call out a Johnson Tee?
How would you deal with a Johnson Tee during a home buyers inspection.
I found one with the vent inside a bay window wall yesterday while fixing water damage from no flashing around a deck to house intersection.
Are you saying this thing is buried in the wall without any access?
Yes it was but we’re going to extend the vent out to exterior wall with 1/4″ slope down per foot. I found a crack in the tee that leaked during drain cycle. Just picked up new abs part and vent cap from Ferguson and will replace both.
Hi,
Does anyone know if the Johnson Tee setup is no longer code in Washington State? Home Depot is refusing to install a dishwasher because they claim code now requires that I install an over the sink air gap. I’d really hate to have to do that, but I can’t find anything in the plumbing code to define what air gaps are allowed.
Thanks.
I know of no amendment to the code to prohibit their use. Ask them for a code reference and post it here if they have one. What you may be running into is that some dishwasher require a drain larger than 1/2 ” which would prevent the use of a Johnson Tee—as they only come in 1/2.” There are still lots of dishwashers that are OK with a 1/2″ J-tee and the Home Depot near me still sells them. Call me skeptical on some amendment to the plumbing code that would prevent their use. The city of Seattle amended the code to allow the high-loop with no air gap device at all—so there is that option although I think it is a bad idea.
Thank you for the response. I contacted the city and they said, “the Johnson Tee is still legal if it has the UPC stamped on it and is installed per manufacturer’s instructions.” I returned a Samsung dishwasher that didn’t have clearance under the unit for the hose and drain connection and I bought a Whirlpool one that did, but I failed to check if it required greater than a 1/2 inch drain. I hope that I won’t have to return that as well. Is there a standard adapter to connect the dishwasher hose to the 1/2 inch drain pipe?
All the dishwasher drains I have seen have an adapter at the end that adapts to a variety of pipe sizes.
Hi there,
I just purchased a house that has a Johnson Tee and looks like it’s been painted over (please see attached).
Like you suggested in your article then, should I just drill small holes in the cap to fix?
Thanks!
While that is in the location of a Johnson Tee, I typically have not seen a threaded one. That looks like a threaded cap and the Tee is typically plastic. It is sometimes capped for the initial plumbing system test, but then the pipe is cut off flush and the decorative cap (pictured in the original post) is installed. I would hate for you to inadvertently find that is a gas pipe for an outdoor grille or something. I recommend you have a plumber sort it out for you.
Thanks for your response!
My home inspector did tell me it is a dishwasher vent, and recommended I replace the cap. I just don’t know where to find one.
Would you still recommend having a plumber come in?
Where are you located? How did your inspector verify it was a J-Tee? Like I said I have never seen one you could put a threaded cap on. Can you check to see if the piece the cap is screwed onto is plastic? Scrape paint away?
He only visually inspected it and didn’t touch.
I’m in Kirkland, WA.
I’ll try scraping the paint off – good idea.
Thanks for your inputs.
The Home Depot around this area have them or Aurora Plumbing. Be careful.
I have a Johnson Air Gap on the inside wall of my kitchen (it does not vent outside like your posts recommend above). It is directly across from my island sink. I am experiencing sewer smell coming from the cap into my kitchen any recommendations? I have a septic tank that was pumped about a month ago and it was after we had the septic pumped we started noticing these odors and found them coming from the “400 Air Cap Trim” located behind my refrigerator. I do have a call into the septic company to see about having the flap at the septic tank checked to make sure it is operating properly.
Is the Johnson Tee still being used or has it been abandoned? In other words, where does your dishwasher currently drain to? If the Johnson Tee is not in use or you never use your dishwasher the trap in the wall for the Johnson Tee may have dried out.
In my opinion, air gaps and Johnson tees are an unneeded redundancy. Most dishwashers have the water inlet higher than the tub level. The dishwashers that fill directly into the sump have a built-in air gap. When the Johnson tee was invented, dishwashers used the same pump for washing and draining, plenty of power to drain. Now all dishwashers have a separate small drain pump for efficiency and noise level, they’re just not designed for the Johnson tee. The 1/2 inch size is not the only problem, it’s also the extra length it adds to the drain. Connect directly to the disposal or drain pipe with a high loop, there’s no possibility of mixing waste and potable.
You may be right, and perhaps why the City of Seattle amended the plumbing code to allow high loops instead of air gaps. I still argue that undless the fill of the washer is higher than the sink rim, there is the potential of contamination. Remote maybe, but possible. I still consider it best practice to have an air gap and since the high loop is going to be necessary, having it run through an air gap is just so simple.
Hi Charles. I want to avoid the dishwasher air gap device on my countertop, but understand its importance. My question is, can it be installed on the wall, like a wall-mounted faucet? I want to place it next to a wall-mounted faucet, which I love because it avoids drips on the countertop. Putting the air gap cap on the wall would cut down on the constant cleaning of water splashes (and its accompanying gunk build-up) that occurs at the base of anything affixed to the countertop around a sink!
A johnson tee can be placed on the wall—provided the washer drains size allows it (not more than 1/2″).
My Johnson Tee is leaking small but annoying amounts of water out the vent hole. Does that mean the device has failed or has some blockage beyond the JT mounting further down the drain? I have no idea how to correct that problem. I would say there’s about a half cup of water that ejects out that vent hole on during the drain cycles, the constant dripping definitely not to the liking of the siding paint. I may have access to what looks like a cleanout port under the sink. Otherwise from the photos of how this is installed that pipe is behind the wall with no way to get at the drain. Appreciate advise and finding rare knowledge of this plumbing technology in Seattle area.
This means you have some blockage in the drain line or the machine itself and it will need a plumber.
Hi, I’m smelling sewer gas from this vent (I’m on the top floor of my condo). I have a Johnson vent above the sink too. Dishwasher drains just fine. I can’t see any piping for wall vent. Can I pour water into the vent hoping it will fill the hidden P-trap if there is one?
It sounds like the dishwasher may be connected to the disposal perhaps instead of the Johnson Tee resulting in a dry trap? Have a plumber check this out.