Dishwasher air gap when not connected to a sink

[Brian Kelsey]

Good Morning!

I have a unique dishwasher installation that needs to be modified for an upcoming remodel.

My current installation has the dishwasher drain plumbed into a shared standpipe with the laundry on the opposite wall, which fulfills the air gap requirement. The standpipe is inside the wall, attached to a "laundry box". This setup has worked well for several years.

We are planning a remodel which will involve turning the laundry area into a bedroom. The laundry box will be removed and covered over with drywall. I would like to leave most of the existing dishwasher plumbing in place, but obviously do not want an open standpipe inside of the finished wall.

This is a single story house with a crawl space. I've thought of a few options, but not sure of the viability or advisability of them
- Could I cap off the stand pipe and rely on the "high loop" for the air gap requirement?
- Could I run a "air gap vent" up through the roof?
- Could I extend it up and terminate in the unfinished attic or in the loop down and terminate in the crawl space?
- I would be fine terminating it above the kitchen counter, but I don't know of any plumbing trim piece that would make it look nice.

I'm leaning most towards the roof penetration, since it would allow a clean out, and keep all the plumbing openings in "wet-able" spaces.

Sketches of the existing installation are shown below. Any input would be appreciated!

 

[Reach4]

- Could I run a "air gap vent" up through the roof?
- Could I extend it up and terminate in the unfinished attic or in the loop down and terminate in the crawl space?
- I would be fine terminating it above the kitchen counter, but I don't know of any plumbing trim piece that would make it look nice.

I'm leaning most towards the roof penetration, since it would allow a clean out, and keep all the plumbing openings in "wet-able" spaces.

I am not a plumber. Your ideas are interesting and a bit amusing. You are considering having the dishwasher pump up to the roof, and to discharge over a standpipe that extends above the roof? I doubt that the dishwasher pump would would be rated for that.

Is the attic "wetable"? I don't think so.

But musing about that roof idea, we have to think about where the p-trap would be. You would not have a standpipe input so far above the p-trap if the p-trap stayed. But why would you need a p-trap at all? Say the pipe rises to the level a plumbing vent would be at. I would see no need for a trap at all. And then there is the fact that the lowest recorded temperature in Longview is -7.0°F (-21.7°C), which was recorded in February. Your dishwasher line could freeze, so that kills that idea.

 

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[Brian Kelsey]

Just to clarify:

I want to leave everything exactly the same as shown in the drawing, except for removing the laundry box. The dishwasher would still drain into the standpipe as it does today.

The easiest thing would be to just cut off the laundry box and leave the standpipe open inside the finished wall, but it would be catastrophic if it ever overflowed. Next easiest is just to cap off the standpipe in the wall, but I'm unsure if that would fulfill the air gap requirement.

I'm looking for a solution that accounts for potential overflow while also fulfilling the air gap requirement.

 

[Kreemoweet]

They make a contraption exactly for the sort of situation you have. It's called a "Johnson Tee", and is a code-approved
method for connecting a dishwasher drain to a standpipe inside a wall. There has to be a vent penetrating one side
or the other of the wall; said vent is basically just a 1" diameter length of plastic pipe which is cut off flush with the wall.
A little cap with holes in it slips inside the pipe, and looks quite nice (IMO). If not obtainable at a local
plumbing supply store, they should be available from various vendors online.

It's barely conceivable that the DW drain could back up that high, i.e. above the flood level of
the kitchen sink. Of course in that event, the backup would exit the vent.

 

[Brian Kelsey]

I looks like I'm going with the Johnson Tee over the kitchen counter.

If not obtainable at a local
plumbing supply store, they should be available from various vendors online.

After an exhaustive search, I found out that it's actually not available to order anywhere locally, or online. I called the Johnson Industries, and they instructed me to mail a $20 check with the ship-to address and material required (PVC or ABS). A bit 20th century, perhaps, but hey, whatever works.

Thanks!