My kitchen sink recently clogged for the first time. I'm sure it will be easy enough to clear the clog by disassembling the trap and clearing it out. I might also replace the existing trap with one that has a cleanout. However, I'm wondering if anyone has suggestions on how to modify the trap to reduce the risk of clogs in the future. I've lived in my home for 2.5 years and this is the first time it's happened after an absence for 6 weeks when the plumbing was not used.

(Another thing I noted is that the dishwasher drain is located after the trap, which from my understanding, is a bad idea and should also probably be relocated.)

plumbing under kitchen sink


As was pointed out, this is an S-trap and not a P-trap. It seems like the easiest solution is to install a sanitary tee and replace the S-trap with a P-trap and an air admittance valve since I don't have a nearby vent pipe available. Does this make sense?

P-trap installation Credit: Illustration by Art Rep Services, Inc.

  • 2
    That's not a p-trap, where are you located by the way, as I think the setup pictured is no longer code compliant in the US. And of course the solution for kitchen sink clogging is a garbage disposer.
    – Glen Yates
    Jul 5, 2022 at 15:50
  • @GlenYates I was wondering as it didn't look like a P-trap to me, although obviously a similar principle. I am located in the US and I know there are many things in the house that are not up to code. I'm slowly trying to rectify this as the previous owner took a lot of shortcuts. Jul 5, 2022 at 15:54
  • @GlenYates I guess this is actually an S-trap? Jul 5, 2022 at 15:56
  • Yes, it is actually an S-trap, even though in your install it doesn't look like an 's'. Search the interwebs for S-trap vs P-trap and you will find a lot of info on what you should have and why s-traps are no longer allowed.
    – Glen Yates
    Jul 5, 2022 at 15:58
  • 1
    Are you sure you don't have a nearby vent? Drain pipes under sinks usually go to a main drain which also has a vent going up though the roof.
    – crip659
    Jul 5, 2022 at 23:20

2 Answers 2


Yes, your edit makes sense: Remove the S-trap and install a P-trap with an air admittance valve.

  • Install the air admittance valve as high as posable (even if you need to offset it to the side/back)
  • Connect the dishwasher above the new P-trap
  • Thanks! This probably should have been obvious, but it makes sense as soon as it was pointed out to me that this is an S-trap and not a P-trap. Jul 5, 2022 at 19:09

For the trap, yes replace the S with a P.

As far as the dishwasher, yes it should be entering the plumbing system above the trap, not below it. In addition, a dishwasher drain must do one of the following:

  • Include an air gap. Basically drain goes up to the counter to a special gadget ("air gap") that has the water then flow back down to the rest of the plumbing.
  • Use a high loop. The drain goes up to the underside of the counter and then back down to the reset of the plumbing. Done properly, this results in an air gap equivalent at the top of the loop.

Sometimes a high loop is used but due to other work or sometimes just neglect the entire drain hose ends up in the bottom of the cabinet. That can result in backflow into dishwasher. Combine that with a real sink clog beyond the trap, and your dishwasher may end up a bit nasty.

  • Any idea how to replace the S with P, it looks like some hight problem there
    – Traveler
    Jul 6, 2022 at 3:52
  • @knowitall I don't think replacing the trap is a problem. My plan is to move the wye for the drain directly underneath the left sink and then put the tee and the P-trap after that. Jul 6, 2022 at 20:39
  • 1
    Good point about the high loop. I did also notice that the drain for the dishwasher was kind of sitting around the floor. I pulled it up, but it's not attached so I probably should get a bracket for that. Also, does the high loop mean that an AAV for the trap is not necessary? Jul 6, 2022 at 20:41
  • The high loop is sort of like a trap for the dishwasher, except rather than to keep sewer gases out of the sink, it is to keep sewer water from backing up into the dishwasher. AAV or traditional vent on the drain (after the sink, dishwasher and trap) is an entirely separate requirement. Jul 6, 2022 at 20:48

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