After flushing, the water level in the bowl drops a bit. It takes about 30 seconds and loses between one and two inches. It starts dropping fairly fast, then slows, then stops, and then the level holds steady until next flush. Bowl still has a nice, respectable amount of water.

No other problems around toilet; no word from person downstairs about leaks or ceiling stains (but haven't had chance to ask them specifically since noticing this). I'm not sure if the floor's level; may slope slightly toward back of toilet, don't have a level handy.

This may even be normal for this toilet (is that likely/possible?)... I only noticed it now, about a week after clearing a clog with a closet auger, and hadn't paid attention to whether it dropped or not before.

About that clog: it was from a toothbrush dropped into the toilet and pushed further down when I tried to pull it out by hand. Auger didn't retrieve toothbrush, but I guess pushed it through to main drain, because toilet has flushed fine ever since.

Do any of these details make it more/less likely to be a leak into the subfloor? And if that is likely, I guess that makes things very urgent, or would it take a long time do any damage? (It'll be tricky to bring in a plumber until a few weeks hence, esp. if that means coordinating with other tenant.)

Apologies for full-on newb questions; this isn't so much DIY as should-I-have-someone-else-do-something, and how-panicked-should-I-be-if-at-all.

  • What happens if you add some (say a gallon) water into the bowl after it has settled? Does it stay full or does it also drift or drop suddenly downward?
    – wallyk
    Oct 20, 2014 at 15:10
  • If I pour a bucket of water into the bowl, it flushes as you'd expect a normal bowl to.
    – Randy
    Oct 20, 2014 at 15:56
  • Sorry, I commented based on memory of trying that before. I didn't observe whether, after the bucket-induced flush the water level dropped again like it does on a tank flush. I'll pour a bucket in soon and answer more properly.
    – Randy
    Oct 20, 2014 at 16:00
  • @wallyk, if I put in a gallon or so of water, then the level will drop just the same as if I'd flushed it (as described in the main question)...
    – Randy
    Oct 20, 2014 at 17:33
  • @Randy Was there every a fix or even an issue? Similar thing happened to me the other day and came up on this post...
    – John
    Jan 16, 2018 at 2:00

6 Answers 6


Open up the back part of your toilet and push down firmly on the flush valve ball (the flap that goes up and down when you press the toilet lever) after you flush the toilet. Your ball/flap probably is leaking a bit and eventually settles after a flush. These can be replaced by following a set of instructions and spending $15.

  • The valve ball seems to be housed inside a self-contained plastic column into which the water feeds, so I can't see or touch the flap itself. However, if the ball/flap were leaking, would the water level in the toilet tank go down after the flush was over, to an equivalent depth of the drop in the bowl? Because that doesn't appear to be happening.
    – Randy
    Oct 20, 2014 at 13:40

Based on all the evidence, I think there is still a partial clog inside or just below the toilet. I would auger it again. Also, check other nearby drains that they are functioning okay.

If other drains are okay, but the toilet continues to be odd, I think it will soon clog when enough stuff is flushed. Pulling the toilet and inspecting underneath may be required.

I think the toilet itself is fine.

  • Glad to hear you think the bowl's fine. My paranoid worry is that in the initial augering I managed through inexperience to damage the bowl and cause a leak. So maybe, just to be safe, I'll leave any further augering to a plumber. Though it would be nice not to foot a huge bill when I could DIY, so maybe I'll give it another shot.
    – Randy
    Oct 20, 2014 at 18:00

If the water level doesn't drop so low that air is sucked through the bowl, causing a 'glurk-glurk-glurk' sound it's likely fine. (That sound is usually indicative that there's a partial clog preventing the vent from equalizing the pressure as the bowl drains.)

  • After the flushing's finished and the water has finished its extra couple inches' descent, it settles and is silent. It's at a height that fully covers the hole at the bottom, with an inch or so of water above that. No glurking. (And I assume the air vent is open because the water wobbles slightly when the wind gets up.)
    – Randy
    Oct 20, 2014 at 14:05
  • Yup, a bit of a bounce is normal as pressure in the line and vent equalize. Not many people notice the water level fluctuating in the bowl with wind- until a hurricane or tornado get close. :)
    – TX Turner
    Oct 20, 2014 at 20:08

I wouldn't expect to see evidence of water leaking outside the pipe, so the ceiling below should remain okay. But this is a surprisingly common problem. Here are most common causes:

  • Some extraneous porous material is stuck in the trap and is "wicking" water over the hump of the syphon. For example, a strand from a string-mop or scrub brush, a piece of cloth, or even a stubborn scrap of paper. I don't think a toothbrush would do this, but I suppose it's conceivable. Snake the fixture trap again to make sure it's completely clear.
  • New fixture installs encounter defective castings more frequently than a reasonable person would expect. Any hairline crack inside the trap section of fixture can cause this symptom. These are INTERNAL leaks, so no water outside the pipe would be evident. Sometimes you can de-install the bowl and find (and even patch) such a hairline crack. I doubt your plunging opened a crack, more likely one was always there.
  • Vent problems - or even windy conditions causing pressure fluctuations - can suck water out of a bowl. (The pattern you described of water consistently sinking slowly but steadily after a flush - without a glug - is NOT typical of a vent problem, more likely it's one of the previous issues.)
  • Partial clogs can mimic (or cause) venting problems as per above.

Its amazing how often cheap toilets come from the factory with internal trap leaks due to cracks in the trap walls. Product exchange under warranty is the best remedy - albeit a dang nuisance!


I had a similar problem over the last day or two. I noticed the level in the bowl had dropped but not so much to allow air in. It would take about 10 minutes to drop. Can see no leaks - floor dry - bowl dry etc. Rung a plumber and he said could be a partial blockage down line and suggested an ordinary sink plunger to force water down the toilet. It appears to have worked. Foe the last couple days the level has stayed constant. So if no visible leaks - before calling a plumber get a plunger and try that first. A lot cheaper!!!


It is a blockage slowing the flow of water drainage. Trap in toilet is 2 - 3" slow leak from flapper will not flow enough to have noticeable effect. Only thing is something slowing down flow through the trap.

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