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dtmbizzle 04-16-2010 11:10 PM

Help with new dishwasher drain backing up
Help please!

Our new basement dishwasher drain plumbing is draining straight out of the air gap/vent. Can't figure out if there is anything plugged up in the piping, but I'm at a loss for what else can be causing it to immediately back up every time it drains out at the end of the wash cycle. Here's a quick history;

My plumbing was all done by a sub-contractor, but I installed the dishwasher, and had it installed perfectly, workgin 100%, draining quietly, and properly. I ran it 5 full times, no issues. Then we had final inspections, and failed the plumbing because our standpipe/drainpipe (sorry if that isn't the proper term) wasn't 18 inches in height. So the plumber came back in, replaced the standpipe, and now it almost touches the ceiling, which seems ridiculous to me, but whatever. Well, since this change happened, the dishwasher drain doesn't work at all. It backs up every time, and shoots water straight out of the air gap/vent. I have tried sticking the drain hose down all the way to the bottom, half way up, just a little bit in there, and I've even tried sticking in in the diagonal air gap/vent hole instead of up top. I'm at a loss for anything other than some obstruction in the U section of the drain...

I don't want to wait for my contractor to get off his butt and get the plumber back over here, and was thinking of just renting a plumbing snake, but I thought I'd ask here, just to see if anyone thinks the setup is wrong, or the arrangement of the pipes is not allowing air/water to flow properly.

Any ideas much appreciated. Here are pictures of the setup. The sink drain works perfectly, no issues there.

Mike Swearingen 04-17-2010 02:07 AM

I'm not a licensed plumber, just an old DIYer, but WHAT in the heck is that drain setup?
IMHO, you need to get rid of that separate dw drain set up completely which is creating the double trap situation. You should only have one trap. If it were me, I would simply put a new tailpiece with a dw hose connection directly under the sink and do away with that open top mess with a hose stick down it.
Good Luck!

Scuba_Dave 04-17-2010 07:42 AM

A plumbing "stack" with an AAV & an OPEN pipe ??
If that is an open pipe then that is not allowed
The dishwasher needs to be a completely sealed drain system

You are being very generous if you call the person who did this a plumber
They have no clue when it comes to plumbing

dtmbizzle 04-17-2010 12:00 PM

Thanks for the feedback guys. The only work I did on this was to connect the dishwasher, all the pipes were installed by the plumber. I guess I'll have to figure it out on my own, but I'm thinking that If I can get a direct, sealed connection into the main large pipe that is in the back (With the white top on it), and just cut away the whole extra assembly, that would work?

I am a RANK novice with plumbing, but confident I can cut/modify this set up... I think. :laughing:

The funny thing is that of course, this exact setup was inspected, and approved by the county...

Mike Swearingen 04-17-2010 12:56 PM

Man, I cannot believe that was approved by anyone.
Go to a plumbing store and get a sink tailpiece with a dw connection on it (you will understand when you see it), cut out that open top stuff, and install the tailpiece to the sink basket and the dw hose from the air gap to it with two ss hose clamps.
Good Luck!

AllanJ 04-17-2010 03:13 PM

Wait a minute.

This is not a double trap, it just looks that way from the camera's vantage point.

dtmbizzle 04-17-2010 11:37 PM


Originally Posted by Scuba_Dave (Post 429814)
A plumbing "stack" with an AAV & an OPEN pipe ??
If that is an open pipe then that is not allowed
The dishwasher needs to be a completely sealed drain system

You are being very generous if you call the person who did this a plumber
They have no clue when it comes to plumbing

Our upstairs sink set up looks very similar to this one, the only difference being that there's a disposal unit/double sink.

I live in Colorado, maybe they do it different here? I don't know, but it looks the exact same, One main pipe with the white topped vent, the sinks draining into it with a U at the bottom, and a second 'stand' pipe with an open top, and the dishwasher draining into it. My upstairs setup isn't isn't sealed, either... The dishwasher drain tube is strapped to the black pipe, but it's not sealed. I went and forced my neighbor to let me check his, too, and its the same set up. We don't live in the ghetto, or anything, so I'm assuming the setup is legit, I'm just wondering if there's anything that could be causing it to back up other than a blockage?

AllanJ 04-18-2010 08:59 AM

I think there is a blockage somewhere.

Is the AAV (the white cover on the other upright pipe) removable? If you were to take that off and the dishwasher now drains OK then the AAV is defective and not allowing proper venting.

If you quickly emptied about 3 gallons (requires some large buckets or pots) into the sink and that took a long time to drain also then you could have a blockage further down the drain pipe.

dtmbizzle 04-18-2010 10:14 AM

Thanks for the reply Allan. I did dump a big fat bucket of water down the regular drain. Maybe not 3 gallons, but it drained super fast. I think i'm going to just snake it sometime over the next few days.

Beanage 09-30-2011 03:22 PM

Same problem in Colorado
Hi dtmbizzle, I too live in Colorado & our house with a 5 year old kitchen remodel has the same set up with a dedicated open air drain that the dishwasher drains directly into. Recently I noticed when the dishwasher does the final drain, about 2 cups of water overflow the open air drain. How were you able to fix the similar problem you were having a year ago?

dtmbizzle 10-05-2011 10:18 AM


I ended up just snaking the drain and that cleared it up. I rented one of one of the autpmatic snakes you hook up to a drill. Problem solved, no other overflows since doing that.

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