A few days ago without warning, my kitchen sink started backing up. From a presumably drained state, it takes about 50 seconds for the water to back up. I've measured the fill rate as one liter in 9 seconds, so the total water that backs up in 50 seconds is 5.64 liters or less, since the drain is slow, not stopped.

My drain pipe seems to be 2" in diameter—though the disposal is much wider than that—so the area of the pipe cross-section is about 16 cm^2. 5.64 liters is 5,640 cm^3, and 5,640 cm^3 / 16 cm^2 is 352 cm, or 3.52 m, or about 11.5 feet if my math is correct.

After trying other things, I removed the P-trap and fed an auger over 20 feet into the drain. No particular debris or residue came out, though there was some black grease on parts of the auger, and the water still backs up at the same rate. With the P-trap off, I am able to hear wind through the drain, so I know for sure that the drain vent is not blocked. If my estimate of the blockage being less than 11.5 feet away is correct, and I fed 20 feet of the auger into the drain, then perhaps my auger went up the vent pipe as in this comment?

Any other suggestions as to what I might try, if I can't locate or identify the obstruction? Is there any benefit to trying any of the liquid drain products? (I believe that I'm not supposed to put them directly into my sink, because of the in-sink disposal, but with the P-trap open I could pour them directly into the drain pipe.) I tend to use enzyme-based build-up remover from time to time, but it's been a while since I've done so, and this began unexpectedly.

  • You're on the right track, but you need to account for the water that normally rests in repose in the pipe. (or that does so because of the clog). Jun 18, 2022 at 22:23
  • Since you tried all and know a lot, it is time to rent one of those scopes and inspect.
    – Traveler
    Jun 19, 2022 at 0:34
  • Are you using motorized auger or manual one ?
    – Traveler
    Jun 19, 2022 at 0:35
  • Just saw your math, Impressive :) you know approximately where the clog is. But the auger should have been much more dirty if you got it in the right pipe.
    – Traveler
    Jun 19, 2022 at 0:40
  • @knowitall I was using a manual auger. Jun 19, 2022 at 2:31

1 Answer 1


All you investigations and assumptions are correct.

However, that the auger came out almost clean say you ended up in the drain vent pipe.

The drain and drain vent are connect with a T junction after the P-TRAP. You are just unlucky that it happens.

Try again, but this time keep turning the auger clockwise as you push it in. The right turn will make the auger wanting to go left or down. Now try the same with left turn

The T split is just a foot beyond the drain connection.

If none works, rent a plumber scope camera.

  • I can see cameras for 3" drains available for rent from the big stores, albeit not in my area, but I've got 2" pipe. Do plumbing supply places rent these, I wonder? Jun 19, 2022 at 3:01
  • @NeilSteiner where are you, so I can look
    – Traveler
    Jun 19, 2022 at 3:08
  • Plenty of supposedly waterproof 16-foot-long endoscope cameras available on the Internet for maybe $40. Might be useful as long as your expectations are not high.
    – Armand
    Jun 19, 2022 at 4:21
  • @knowitall I ended up using a slurry of baking soda, followed by white vinegar. That managed to really stop things up, but copious amounts of additional white vinegar, plus some judicious use of the disposal to push the water down managed to clear things up. There is still a little bit of unusual behavior, but I think that if I treat the sink with an enzyme product over the next few days, I may be able to resolve the matter entirely. Jun 20, 2022 at 1:44
  • @NeilSteiner good choice
    – Traveler
    Jun 20, 2022 at 1:49

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