installing a standpipe drain for dishwasher

i am planning on adding a dishwasher to my kitchen where there is no dishwasher now. the location that i have available is to far away to run a drain hose to sink drain. so i was going to put a standpipe drain in with a p trap and a air gap. my question is, the easiest connection to a drain in the basement, is the 3" stack drain from the upstairs bathroom, can i do this by just cutting a section out of this stack, putting a y fitting on with clamps, and connecting standpipe drain into this? i can also route the drain over to the 1.5 drain line for the kitchen drain, but is very busy with electrical wires, and i would like to avoid this route........thanks

You can put a p-trap in for the dishwasher off the 3" stack, as long as you vent between the stack and the p-trap.
If you can't tie the vent back into another vent, you will at least need to use an AAV on it.

thanks for the info,,,,but ,,,what is an aav?

Air Admittance Valves (AAVs)

The purpose of vents is to allow air to enter the plumbing drainage waste and vent system and equalize pressure when water drains out of the system maintaining the integrity of the water trap that prevents sewer gases from entering the building through fixture drains.

https://ipscorp.com/plumbing/brands/studor/

Terry,,,,,a couple of questions about your advice with the standpipe. How high does the standpipe have to be above the p-trap? Once I have the standpipe and p-trap set up, can I run a piece of 2" pipe down 4 or 5" and attach my aav vent, and 45 it down thru floor to connect it into my 3" stack? Does the aav vent have to be the same height as the stack, or does it have to higher? Is the purpose of the standpipe to give the p-trap a chance to keep up with the drain water coming out of dishwasher? I am planning on doing all this plumbing behind where I want to install the dishwasher.....thanks......Karl

The AAV must be installed in a serviceable location as high as possible above the flood rim of the fixture it is servicing. It should not be installed behind the dishwasher or in the wall. I would think for you application you should use a countertop airgap for a dishwasher, they are required in some areas. You also need to find a picture of how a vent, in your case the AAV, should be installed in connection with a P-trap, you do not want to end up creating an S-trap, what you wrote would be wrong. The stand pipe does have a minimum and maximum height it can be above the P-trap. Codes vary. I'm sure if Terry reads this maybe he can provide a diagram or picture of an AAV and P-trap install.


I found this example, remove the sink and add the hose fitting for the dishwasher.

When you say the sink is too far away from the dishwasher, what do you mean? is it in the same room? Is it a very large room? I mean, you can run under the floor and I'm not aware of any distance limitations.

It seems to me that putting a trap in the stack in the basement below upstairs toilets and so on could cause a far worse problem than you can imagine, aside from being against code. Wet-venting a p-trap below the toilet is very bad practice.

And an AAV or other vent won't stop a plugged drain from causing sewage to come out at the new lowest level - your new trap.

He should be coming up to the level of the dish washer for the P-trap, putting it in the basement would make the stand pipe too long. He should come into the cabinet next to the dish washer and put the P-trap and AAV, like in the picture. He also needs the air gap. There is a limit to the length of drain hose.

Yes there is a limit, according to the instructional manual (I tried to attach a copy of the specs ) The distance is not more than 12', but there are too many cabinets in the way to run the drain line correctly. To get to the drin for the sink, I would have to drill thru the back of all the cabinets, and also there is a stove in the way, which I would have to figure out how to get around that. I was going to install trap above floor level, but was a little confused as to how to lay out standpipe-p-trap-air vent. I do appreciate the pic you sent of the AAV. I aggree with you Herk as far as taping into the 3" stack for the upstairs toilet. I going to figure a way to tap into the 2" line for the kitchen sink. When running my 2" pipe to this drain, I should try and avoid any 90 degree elbows right? thanks

In new homes, I often ran the dishwasher hose under the floor when it was not next to the sink. However, that wouldn't work well with a finished ceiling below it.

You don't have to completely avoid 90* elbows, you just have to know when to use them and how, and which ones to use.