Strange Toilet Leak


Introduction: Strange Toilet Leak

About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

Water leaks in a toilet should not be complicated, but sometimes disguise or hide themselves in ways that perplex. I just fixed a leak I had never seen in all of my years as a homeowner. The leak was caused by granules of rust that kept the flapper from sealing fully. The rust came from the steel arm which connects the ball float with the fill valve. See later steps for details and photos.

Often the flapper at the bottom of the tank (red/pink round device) deteriorates. The rubber becomes rough and granular. It looks good, but rubbing its underside leaves a dark stain on your finger. Or, the fill valve (white device with four corner screws) does not seal and water constantly runs into the tank, although slowly.

In the case of a flapper leak you may hear no noises punctuated by the sound of the tank topping itself off. Often the house needs to be completely quiet for you to notice. In the case of a fill valve leak you hear a faint sound of water flowing continuously.


  • 1/4 inch aluminum rod


  • Hacksaw
  • 1/4 x 20 thread die and die handle tool
  • Magnetic grabber

Step 1: What We Noticed

A while after the toilet fill valve has shut off, the porcelain above the water line should be dry and there should be no ripples on the water surface.

What we saw was moist porcelain with faint signs of moving water. There were faint ripples on the surface of the water. See the text boxes on the photo. There are signs of ripples and faint water flow in the photo because the fill valve just shut off. Water is still draining slowly from the rim holes below the toilet seat. But, after a short while the porcelain should be dry above the water line and the water should be still with no ripples.

We replaced the flapper, but the signs of leakage continued.

Step 2: Rust

The bottom of the toilet tank shows a number of different stains and discolorations. Recently, though I noticed shards of something, especially around the flapper. Something made me wonder if it could be rust, perhaps from the bolt heads that hold the tank to the base of the toilet. I worked at removing the rust pieces as best I could. I found I needed to do this more than once.

I moved a magnetic grabber on the bottom of the tank and noticed the shards clung to the magnet. Most of the shards were too large to migrate and disturb the seal between the closed flapper and its base. But, there were probably finer pieces of rust that did lodge under the flapper and disturb the seal. That would cause the very slow leakage we had been noticing.

Step 3: The Source of the Rust

The photo shows the old steel arm between the ball float and the fill valve. I had overlooked it and never gave it any thought. But, once I noticed it, I could see how diminished the diameter of the arm was. Much of it had rusted away.

Step 4: Aluminum Rod

I could have replaced the old steel rod with a new steel rod, but wanted something that will not rust. A trip to a store found none of these rods available in that store. I had some 1/4 inch aluminum rod left over from another project. It will not rust. I sawed a piece of the rod to the length of the original steel rod and cut threads on both ends. (I am accustomed to cutting threads on steel. Usually, the die will pull itself farther onto the rod. But, the aluminum is soft. I had to exert a constant downward pressure to keep the die moving forward and not destroying the threads already cut.)

Step 5: All Done

I put my new rod into place. I did need to bend it by hand a little so the float ball did not rub on the side of the tank or catch on the raised flapper, also to set the water fill level. I eventually replaced the rusting bolts on the bottom of the tank with solid brass tank bolts from the local hardware store. (Scale and rust were still coming off of these bolts, and there was still a little leakage showing in the bowl.)



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    8 Discussions

    "newer" toilet valve components have no metal parts or a float at the end of an arm. They are all plastic with rubber gaskets. The float surrounds the water supply valve mechanism and uses a plastic lever to shut off the water. The "newer" valve has more adjustments to fit more configurations than the older versions.

    2 replies

    I did install one of those newer ballcock designs oin another toilet. I also wanted to explain that granular material mysteriously appearing on the bottom of the tank can get under the flapper to cause a strange leaking, and that granular material could be from rusting components a DIY person can replace with his own parts he made.

    Absolutely! Toilets are so essential but sometime they act like they are possessed! I recently was called by a friend that had a toilet that would "scream" on occasion at random times, day or night. It was a small leak through the shutoff valve controlled by the float!

    Thanks for the description.

    I had a similar leak, but it was caused by the underside of the flapper valve developing small water-filled bubbles or blisters. After I popped them with a pin and squeezed out the water the problem was solved. (Normally I would have replaced the valve, but it is an expensive brand that uses its own - expensive - rubbers.)

    Phil -- great write-up, as usual! I once had a toilet that would periodically "top itself off" just like you would expect with a leaky flapper valve. I replaced the flapper valve, cleaned around where it seats, but still had a problem. Finally, using a flashlight, I saw that the overflow pipe had a small crack near its base, which let water gradually leak out. Toilets -- can't live with them, can't live without them....

    1 reply

    Thank you. I appreciate the information about the unusual leak you found. It is nice to hear from you.

    Great description of the trouble-shooting process. I'm more used to the flush siphon than than the flapper valve, so it's nice to have a walk round the bits. Very clear, thank you.

    Toilet replacement parts are mostly bogus. You do need a magnet to check "bronze" tank bolts, most are simply plated steel. The arm of the float, if your system uses that design is, as you have found, ferrous metal also. Sometimes minor leakage can be solved by simply wiping the valve seat and disk contact area, a place where "slime" seems to easily grow, but when replacing the flapper itself, I prefer the red ones over the black, they seem to last longer.