I'm trying to install the waste lines to attach my sink to the sewer line. This is complicated by my garbage disposal being directly in front of my wall hubs, forcing me to divert the lines around the disposal. I also need to leave enough room to attach an Air Admittance Valve.

I was hoping I could get some guidance on how to configure my waste lines so they're compliant with the IPC.


Relevant components:

  • Sink
  • Garbage disposal
  • 2" hub**
  • 1.5" hub**
  • Dishwasher

** 2" hub drains in 1.5" hub behind the wall

enter image description here

What I've Tried

I've dry-fit 2 configurations that seem plausible but I'm totally open to other ideas.

Configuration 1:

Fittings from P trap to 2" hub:

  1. Long sweep (1.5")
  2. Sanitary Tee (1.5", 1.5", 2")
  3. 1/8 Bend (2")

The AAV is attached to the top leg of the sanitary tee with 2 1/8 bends.

The dishwasher hose is inserted into a Wye, just below the counter top. The dishwasher line is connected to the 1.5" wall hub.

enter image description here

One issue with this configuration is I might not be able to get the P-trap high enough to maintain 1/4 in/ft

Configuration 2:

Fittings from P trap to 1.5" hub:

  1. Long sweep (1.5")
  2. Wye (1.5", 1.5", 1.5")
  3. 1/8 Bend (1.5")
  4. Long sweep (1.5")

The AAV would be attached to the 2" sewer line above the sink level.

The dishwasher setup would be similar to configuration 1 except the flow merges with the garbage disposal with the wye.

enter image description here enter image description here

I should be able to get the P-trap to an appropriate height for this one. I'm just not sure if it's code for me to attach the AAV to the 2" hub instead of closer to the trap. I'm also not totally sure about merging the dishwasher line with the garbage disposal but it seemed to be OK based on my interpretation of the IPC load requirements for 1.5" pipe.

  • Why do you appear to have two separate different size drains stubbed in from the wall? Is one a vent? What is that other pipe coming down on the left? Is it a vent? If it is, why does it have a P trap on it? What is the additional pipe coming down back middle? Why is it not connected in the second configuration?
    – K H
    Apr 29, 2021 at 4:08
  • two p-traps is crazy. Apr 29, 2021 at 7:12
  • @KH I'm actually not sure why there are 2 separate wall drains. They were there when I bought the house. I don't think either are vents. The top wall drain just runs into the bottom one (I can confirm by observing water in the bottom drain when pouring from top) and is only connected to one horizontal run behind the wall. The left pipe (on the right in the photo) is the drain for the dishwasher (high loop). That is connected to the bottom wall drain. The trap in that leg is due to the dishwasher and garbage disposal being connected to different drains. Back middle pipe is the vent (AAV at top)
    – Brian
    Apr 29, 2021 at 15:48
  • cont'd: back middle just isn't shown in the 2nd config (didn't have parts to mock it out) but it would be connected to the top wall drain and hold the AAV. For some context, this is a reinstall. Configuration 1 is similar to the setup when I bought the house, same main features but more complex routing since I have less room now. I've been setting up the dishwasher drain like this to match the previous install but could I just keep the high loop and connect it to the top connection on the garbage disposal and get rid of that whole run? I couldn't find any restrictions in the IPC.
    – Brian
    Apr 29, 2021 at 16:02
  • @FreshCodemonger are two P-traps crazy in configuration 1 where one is connected to the top wall drain and the second is connected to the bottom wall drain? In configuration 2, would you suggest having a single P-trap before the wye?
    – Brian
    Apr 29, 2021 at 16:08


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