I’m a newbie homeowner who continues to experience a minor plumbing issue.

My toilet has a slight leak where the water supply line connects to the toilet fill valve. I replaced the gasket inside the tank, as well as the connector pipe itself from a plastic one to brass one, but nothing has changed. I tried tightening the nut a little more, and that slightly slowed down the water drop, but it still leaks. Since it doesn’t leak at all when I turn off the valve, I was confident that replacing the pipe would fix the problem and now I'm kind of lost.

The following image found on the internet illustrates the location of the leak:

enter image description here

The water is leaking between the nut and that flat white plastic part that is screwed right below the tank.

Note: This is not an actual photo of my toilet. I’m using the photo to clarify where the leak is.

The actual supply line I purchased is this:


BrassCraft 3/8 in. Compression x 7/8 in. Ballcock Nut x 9 in. Braided Polymer Toilet Connector, Model B1-9DL F

  • Did you inspect the porcelain for irregularities (bumps, holes)? Could be that the gasket simply can't accommodate a rough area in the hard surface.
    – isherwood
    Commented May 17, 2016 at 14:51
  • How is this leak manifested? If it were the gasket, I'd expect a leak whenever the tank is full. Or do I have the wrong gasket? Commented May 17, 2016 at 15:14
  • Hi, I edited the question with picture, does it clarify? I don't see any irregularities in the porcelain, and it is not leaking from the tank itself. I know this because I completely disconnected the water supply pipe and there is no leak from the tank even when it is full of water. There is leak only when I turn on the supply valve.
    – 290chan
    Commented May 17, 2016 at 16:56
  • It is similar to this post, but I replaced the pipe like OP did and the problem still exists. diy.stackexchange.com/questions/27728/…
    – 290chan
    Commented May 17, 2016 at 17:46
  • Is the brass pipe in the photo the new one after replacement? It looks pretty grotty and dinged up. Commented May 17, 2016 at 18:36

4 Answers 4


The original leak is most likely either caused by a failure in the rubber washer that connect your supply line to your fill valve, or a leak in the seal that connects your fill valve to the tank.

This is a common problem, especially with older toilets that use natural rubber washers. The rubber breaks down over time and will eventually begin to leak. The newer synthetic washers will last much longer.

It is unfortunate that you already have taken it apart because you will have a harder time determining the source of the leak. When you run into a leak of this kind, it is best to first check the supply line itself, as it is the easiest to access. Shut off the water supply, and drain the tank of water. Then unscrew the supply line and inspect the washer. It should be firm and flexible, yet hold its shape and be in one piece. If it is not, then it needs to be be replaced and you can reinstall the supply line. After a quick test, you should be able to see if this fixed the leak. If it leaks from the supply, make sure that the washer is in place. On Occasion, the washer is missing right from the beginning. They either fall off, or people take them off.

The other place it could be leaking is from inside of the tank. You will need to disassemble the toilet as above. You will then needs to loosen the retaining nut on the outside bottom of the tank where the supply line goes. Loosening this nut should allow you to lift out the fill valve. Inspect the washer on the valve, and check if it is good. Also check the threaded part to make sure there aren't any cracks in the fill valve body as well. Replace washer, and reinstall.

By replacing both of these washers, it should solve the leak. If it doesn't then there may be a fault in the parts themselves - either the supply kine is bad, or the fill valve, or possibly a combination of both. Also be sure that it is leaking from the supply, and not from anywhere else. There could either be a crack in the porcelain, or there could be a bad tank to bowl seal. There are "universal" rebuild kits available out there that include everything that you need to rebuild a toilet. They include all washers, fill valve, and a flapper. The only part that is not included is the supply line. If the internals of the toilet are old, or not functioning properly, then it would be a good idea to do an entire rebuild.


I would replace the supply line with a flex line this will give you a new nut and seal and the flex ones don't have as many problems as the solid lines. These are cheap and easy to replace.

  • Thanks. The one I got is actually flexible one, sorry for misleading photo. I think mine is this: homedepot.com/p/…
    – 290chan
    Commented May 17, 2016 at 20:24

Use Teflon tape on the treads if the gasket inside is not working properly.

I suspect because you have a new supply line that the upper nut, white in the photo, could be the problem. It holds the fill valve mechanism inside the tank securely to the porcelain tank, if the gasket ( inside the tank at the bottom of the fill valve), is damaged or is simply not tight enough then water could be leaking out of the tank. You could replace that washer and maybe use some plumbers putty between it and the porcelain.


Be aware you can also get hairline cracks in the plastic shut of valve. I just had to replace the valve because of this issue unlike the easy to get at fittings shown.

I had to deal with a solid one-peace porcelain body with connection at the rear under the cistern. Wonderful job and one you can not achieve without a plumbers wrench patience and will.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here. Commented Mar 15, 2020 at 9:22

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