Combo dishwasher and sink clogging into one another. Drains lower than wall drain. I need corrective action help.

[NotAPlumber50]

Hello Everyone,

I have a newly installed dishwasher and sink. As with the sink, the dishwasher drains entirely using gravity. Recently the sink became clogged just after a week of install. It would slow drain, until one day we opened the dishwasher, and it was filled with rotting water. I hired a contractor which included plumbing and I'm pretty confident It is wrong. They were not cheap, I don't know where they got the plumber. This plumbing job alone cost me almost $1,000. I'm going to get the plumber to fix it, but I'd rather have something for them, than have them mess it up again.

This is how it was plumbed and the result

It worked great when it was just water and I let them go, but the pipes clogged after a bit of food debris. Does anyone have any ideas on how to fix this??? It's hard to see but the dishwasher drain is lower than the wall drain, since the dishwasher has no pump, it leads me to believe that this is unfixable. I am of the opinion the plumber knew this was going to be an issue but didn't want to have to tear the wall away or cancel the job.

I know moving the wall drain lower is the obvious answer but that sounds like a lot of work, I have no clue what's behind those walls. The drain connection is PVC, but I know at some point it goes to metal. In fact, I think that's where the clog occurred to be honest (but the above still needs to be fixed). I can't see it in my basement, so I believe that coupling might be behind the plaster walls.

I am proposing the below:
1. Essentially cap the sink cabinet wall drain shut
2. Sanitary tee for joining the dishwasher drain to sink drain
3. P trap off the tee, downward slop of about 6 in to slow down water
4. Vertical pipe that leads to PVC Wye
5. Wye connects to PVC drain that's coming from the 1st floor tub / toilet.

I am debating if there needs to be an AAV. This is a rental so the less stuff that can fail, the better. The main drain shares the same wall as the kitchen drain and I'm pretty sure the kitchen cabinet wall drains, and main drain are less than 5 feet apart. This means it is not needed right? How long should the p-trap tail be so that it doesn't get siphoned.

 

[NotAPlumber50]

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[Bannerman]

Don't understand your comment about the dishwasher having no pump. Dishwashers use a pump to circulate the water from the bottom interior pan, through the spray nozzles. The same pump is utilized to discharge dirty water to drain during each drain cycle.

The only way I could see a DW not utilizing a pump to discharge the drain water, would be a small chamber DW which sits on the counter top.

The best method to prevent the condition you are experiencing, will be to install a dishwasher drain air gap device as shown in the image below. The air gap device will be typically located behind the sink, located directly on the sink's rear apron, or directly through a solid surface counter when an undercounter sink is utilized.

With the air gap device, the dishwasher pump will pump the drain water into the device chamber which protrudes above the height of the counter top. Once there, the water will drain by gravity through a larger diameter hose which is connected to the disposal inlet or drain connection below the sink. Because the drain connection directly from the dishwasher is separated within the chamber above the height of the sink, even if a sink drain backup results in water overflowing onto the counter, no water will drain back into the dishwasher.

When an air gap drain device will not be utilized, most dishwasher installation instructions state to raise the DW drain hose as high-up and close to the underside of the counter top as possible (high loop) before lowering to the drain connection. In this manner, a sink backup will be less susceptible to drain back into the dishwasher, unless the water in the sink rises fully up to the level of the drain hose just below the counter top.

In addition, it appears your existing DW drain connection, is connected to the trap arm after the P-trap, whereas it should be connected above the P-trap, as depicted in your diagram.

 

[Reach4]

It seems probable to me that there is a vent in the wall. Lack of a vent does not cause lack of draining; it causes smells.

So I suspect that you may have a clog. If you do serious piping changes, you should make it easier to remove clogs.

I sure don't like having those two glued 90s. I think one glued 45 at the wall, and the trap adapter glued to the 45, would have been the much better routing.

Minimally, I think the drain line should be snaked out. Then a new slip joint trap would be placed. The connection between the sink and the input to the trap would be a branch tailpiece. https://www.homedepot.com/p/Oatey-1...ailpiece-Plastic-Slip-Joint-HDC9698/315724875 The dishwasher hose would connect to the branch input to the tailpiece with one of the methods Bannerman suggested.