Johnson Tees and Countertop Air Gap Devices

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.

Air Gap Device plumbed backwards

Air Gap Device plumbed backwards

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.

Bay1 041

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.



Charles Buell, Seattle Home Inspector

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  1. 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?

    • Charles Buell says:

      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.

      • Charles Buell says:

        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.

      • Charles Buell says:

        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.

  2. 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?

    • Charles Buell says:

      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″

  3. Jorge Mendiguren says:

    Where may I buy a Johnson Tee?
    Thank you.

    J. A. Mendiguren

    • Charles Buell says:

      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.

  4. 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

    • Charles Buell says:

      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.

  5. dwight perkins says:

    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”

  6. Dan Hemenway says:

    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)

    • Mitch Lacey says:

      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.

  7. Stephanie says:


    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??

    • Charles Buell says:

      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.

  8. 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?

    • Charles Buell says:

      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 🙂

        • Charles Buell says:

          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 ;).

  9. Kevin Warner says:

    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?

  10. Kevin Warner says:

    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.

    • Charles Buell says:

      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.

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