Sink trap / disposal quiz

Plumber friend sent this to me quizzing me. What’s wrong in this pic?


Looks like the disposal drain outlet is lower than the wall connection, so it runs uphill.



Nice “Low Loop”!


Probably should have the disposal at the smaller (right) sink. Make the plumbing much easier.


Winner Winner chicken dinner. Except I’m having ham.

Disposal wasn’t draining and yes Disposal should go on smaller sink.


That is what you saw wrong with this configuration :roll_eyes: I thought Ryan and Jeffrey nailed it!


In his defense, the disposal could never work as-is with where the drain is exiting the cabinet. The easiest fix at this point would probably be moving the disposal to the other sink.

Ryan it’s hard to tell with the camera angle so it’s moot. Lower the camera angle and all is good.


Piling on here:

  • Is there a high loop for the dishwasher? Or an air gap?
  • Is the highest supply valve (red handle) leading to dissimilar metals?
  • Anyone else dislike the cord for the disposal, which could readily be snagged, damaging the plug?
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Yes! even the bowl depths look different from that picture angle!

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I’d like to know how the plumber got this joint not to leak. The lower portion of the return bend is beveled and isn’t made for the extension tailpiece. I’ll bet it’s only in by 1/8” and the slip nut is very tight.


1: Tail piece length. Research has proven that limiting the tailpiece length to “24 inches” will help to eliminate the possibility of the trap to self-siphon.
2: Disposal should be on the other sink.
3: No high-loop.
4: trap fitting looks irregular.
5: Partial S-trap.

6: Weir Seal

There’s a loose wallbox and receptacle with a missing plate and romex subject to damage for what may be the grey appliance cord for the disposal behind this plumbing mess. Not sure what the black cord is for…maybe the dishwasher??

Plus, it’s hard to tell, but it looks like the pull-out faucet may be wrapped around the disposal drain line and the dishwasher supply line.


That’s because they ARE different.

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I know, that’s why i made that statement

Yep. There’s a lot more wrong than right. Jerod said it was basically a complete do-over.

I got burned on a trap once years ago and had to pay a plumber a couple hundred bucks to fix it since the pipe’s entry point in the wall had to be lowered. Everyone wants deep sinks these days and the plumbers back in the 70s didn’t know/care so they put the wall outlet 16" above the bottom of the cabinet!! After paying a lot more attention under sinks it’s amazing how often things are messed up.


19.5” from finished floor was the normal back then. Today everyone has a deep bowl and it’s best to shoot around 16” and add an extension tailpiece if the customer goes with a shallow sink.

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That’s funny… I never realized there was a standard. It seems to be all over the place on older houses. So, 16" above floor = +/- 10" above the cabinet base? That’s a lot of space for a trap. I guess someone was looking out for space to store sponges? I always just figured plumbers didn’t want to bend over and expose their ass cracks… wait, never mind.

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