Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

In my toilet, when the shut off water valve is open:

enter image description here

Water leaks above the coupling nut:

enter image description here

If I close the supply water valve and the tank is full, there is no leakage. What could be causing the water leakage? The water supply line is less than a year old. I also taped the connection where the coupling nut screw over and it is still leaking.

Is it possible that the water supply line is broken at the nut? Should I get a new one? The supply line I have has a plastic nut and is flexible.


There was actually a hairline crack in the plastic tube that comes out of the tank to the outside. The plastic pipe was replaced with a brass one to fix the issue.

share|improve this question
up vote 0 down vote accepted

The washer under the nut is probably leaking and the easiest/best solution's would to be replace the pipe.


The reason it only leaks when you have the supply on is that there is no significant back pressure on the fittings from the tank as the tank has an air gap and the filler is at the top of the tank not submerged at the bottom ( which would cause back pressure)

P.S. DON'T use mutigrips, use a spanner or shifting spanner, on a plastic nut (or even brass) you can deform the nut by the crushing force of the mutigrips as you tighten the nut.

share|improve this answer
Is the pipe the water supply line as shown in the pictures? – Thierry Lam May 11 '13 at 0:16
yes. and you could replace the washer or use teflon tape to seal it or just replace it with a braided flexible connector (easy hooker) – UNECS May 11 '13 at 12:26

Yes, that is the supply line. Believe it or not, in those types of fittings, the tighter you tighten the connection, the greater the chance of a leak. They are typically compression fittings using either a brass compression ring or a rubber type of washer that compress when tightened. They should be hand tightened then snugged (1/4 turn more) with an open end wrench, adjustable wrench (shifting spanner).

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

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