I'm running a drain for a utility sink off of a stack in my basement. I wanted to know if it's ok to have a 90 degree elbow going up then out to the utility sink since when the water drains it's going to have to go back up the 90 degree elbow to the main drain. I've attached a picture.

enter image description here

The drain then runs to the left to a secondary drain line that runs vertical in my basement. Just not sure if you are allowed to drop a 90 degree angle like this since the water would have to go up when I use the utility sink.

  • 4
    Only in locales that do not experience gravity.
    – bib
    Feb 5, 2016 at 20:39
  • Thanks for the sarcastic remark but shouldn't it work just like the p trap where the water gets pushed up as more comes through?
    – Greenhoe
    Feb 5, 2016 at 20:40
  • Does the horizontal pipe along the wall flow downward? You have created your own P-trap like device, but I'm not sure if it's allowed by code. Can you have P-traps in the wall?
    – JPhi1618
    Feb 5, 2016 at 20:43
  • 2
    If you add a p-trap to this pipe you have the problem discussed in this question. If this is in place of a p-trap, you have a lot of water to move and risk solids being trapped in the lower horizontal run.
    – bib
    Feb 5, 2016 at 20:47
  • 2
    @JPhi1618 Traps can be in the wall (think about a second floor tub/shower). However, according to code, traps have to be self cleaning, which this contraption would not be.
    – Tester101
    Feb 5, 2016 at 22:41

2 Answers 2


No, you should not do that. As mentioned in a comment, the drain is going to fill up with gunk and clog. Depending on use, you'll find that you have to snake this line quite often.

While traps do hold water, they are limited in the depth of water they can hold. Traps are also designed in such a way, that normal use stirs up any "sediment" and helps flush it away (self cleaning).

Uniform Plumbing Code

Chapter 10 Traps and Intercepters

1003.0 Traps - Described

1003.1 General Requirements. Each trap, except for traps within an interceptor or similar device shall be self-cleaning. Traps for bathtubs, showers, lavatories, sinks, laundry tubs, floor drains, urinals, drinking fountains, dental units, and similar fixtures shall be of standard design, weight and shall be of ABS, cast brass, cast iron, lead, PP, PVC, or other approved material.

I'm not sure how far away the vent is for this fixture. If that's 2" pipe, it has to be within 8' of the trap weir. If it's 1½" pipe, the vent has to be within 6' of the trap weir.


yes, it would be like a p trap that is always full of water. Risky because of the joints there.

  • 7
    Not risky because of the joints. Risky because of poor flow and sediment buildup.
    – isherwood
    Feb 5, 2016 at 20:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.