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.

Rough-in plumbing for a Johnson Tee air gap device

Rough-in plumbing for a Johnson Tee air gap device

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.

Nice exterior finish cap for a Johnson Tee

Nice exterior finish cap for a Johnson Tee

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.

Capped Johnson Tee

Capped Johnson Tee

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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Comments

  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”

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