I have a kitchen sink that slows down and clogs every few months. Every time I could snake it, but it gets clogged again after few months. The build up is mostly oil. I suspect the pipes have too many unnecessary turns, causing the problem. Please see the attached pictures, where I marked out the water flow in yellow and orange arrows, also marked the build up in green. Overview: Overview

illustrated: illustrated enter image description here

My question is, is this installation optimal, or needs improvement? Does below picture show a better way? Thanks in advance!


  • Rule #1 NEWER put oil and grease in the sink. Use a separate container with lid to collect it and dispose.
    – Traveler
    Commented Jun 18, 2022 at 20:14
  • +1 for the pictures and drawings
    – Traveler
    Commented Jun 18, 2022 at 21:24
  • @knowitall thanks for your comments. I am not dumping any amount of oil, but you know, there is always some oil in the bottom of plates/bowls/pots.
    – Guang Yang
    Commented Jun 20, 2022 at 23:42
  • It will accumulate over mots of use, salat oil, frying pan oil and other sources of oil. I do not. think you dump oil in there on purpose, it just happens. Here is a test: do you have oil collecting plastic container (with lid) next to the sinck ? to drain oil in it ? If not you should.
    – Traveler
    Commented Jun 21, 2022 at 2:30
  • To what extent shall we collect the oil? Say you have finished a nice spaghetti and meat ball with marinara sauce, or simply a slice of pepperoni pizza, do you wipe the plate super clean or do you simply rinse it, before putting into your dishwasher?
    – Guang Yang
    Commented Jun 23, 2022 at 17:37

2 Answers 2


I suspect the issue might be with the pitch of pipes. The green sections look like they may not have enough downward pitch for all the liquid to flow downstream, and so some puddles in those areas and eventually forms clogs.

Standard downward slope for waste pipes is 1/4" drop per foot of pipe or 1.19 degrees. An inexpensive small level called a "torpedo level" usually has a lengthwise notch so you can set it on a pipe, but for a small angle like 1.19 degrees, it might be easier just to get a "clinometer" app for your smartphone, set the phone on the pipe and read the degree angle directly.

Since you have a lot of drains in a fairly compact space, it might indeed be best to get a professional with experience to fix/rebuild your undersink waste pipe system.

  • Thanks! Shall I hire some professionals to make it right, or is this a simple DIY job?
    – Guang Yang
    Commented Jun 20, 2022 at 23:43
  • @GuangYang on the left sink, there is a screw fitting that you should be able to loosen. You may be able to lift the plumbing slightly then tighten the fitting and hold the whole thing in place just a bit higher. That would help with the slope. I can't tell for sure if there is a screw fitting on the right side coming out of the disposal. Whoever installed that glued most of it and did you no favors - usually the P-trap is all slip-nut couplings so they're easy to disassemble when you need to.
    – FreeMan
    Commented Jun 21, 2022 at 17:06
  • Thank you @FreeMan, will check out the screw fitting
    – Guang Yang
    Commented Jun 23, 2022 at 17:38

Yeah I agree completely with Armand... the areas you have identified with green are all too level. This is definitely something you can do!

I don't think you need to change the arrangement, as in your second diagram (it's very much standard)... the key would be to raise the trap (the downward loop) on your left sink. You may have to disassemble it and trim the bottom of that top white plastic part to raise the first trap up... that would raise the whole slope of everything.

These drainage tubes are thin-walled and the system allows for some slop because it's drainage (non-pressured). But it can be a bit aggravating.

The traps are there (and in your toilets) to create a natural water blockage for odors coming from the sewer line... kind of genius, but they can get stopped up.

From your diagram, I assume you've already disassembled it and cleaned it (yuck, right?) I think the key is raising that left trap by shortening the first plastic element on the left sink.

And it's best not to pour grease down the sink... not just for your plumbing, but for the water treatment plant – it screws up their system, and is a constant problem. Best to let it cool in a pan or bowl, then scoop it into the garbage. Light oils are fine, but animal grease is a problem (a good friend of mine is a wastewater plant engineer).

Best of luck... btw, I don't think I've ever seen such a pristine sink cabinet :D

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