Toilets, Sinks, Showers, Tubs and Disposals - mansfield toilet slowly running

Hey guys, new to the forums so thanks for having me.

I've been working on a Mansfield toilet that has a very slow leak, from the tank into the bowl. I originally just replaced the seal in the flush valve because it seemed worn out. Didn't fix the leak. I took the tank off and replaced the entire flush valve assy with a brand new one, still same issue.

So I bought a Fluidmaster setup (similar to the one here Fluidmaster | Products| Flush - Flush Valve (507A,507C) (http://www.fluidmaster.com/html/flush_products_507c.html)) and installed that. The rubber stopper seems to make a much better seal with the hole that feeds into the tank than the Mansfield stock one, but I still have a very slow, small leak that runs into the bowl.

The only thing I can think of is that the seal where the valve sits in the hole at the bottom of the tank maybe has a small leak. I didn't use a giant wrench to tighten the nut that threads around the bottom of the assy from below the tank and sits in the hole that feeds into the bowl. But, I did tighten it by hand and it doesn't seem like it will get much tighter even with a wrench.

Any ideas/suggestions?

How did you determine you have a leak...what were the symptoms?

You may have a crack in the tank where the flush valve seats. Also make sure the hose into the overflow isn't pushed down too far. It can siphon out of the tank if it is.

If the hose is ok, you could take the tank off and set it over a bucket, sawhorses, or some woodblocks, fill it up by hand and see what you find.

I can verify the leak by looking in the bowl. It's very a very slow, small leak, but you can see the water leaking into it.

I'll double check the hose, but when I installed it, it sat right at the top of the overflow so I'm not sure that would be it.

The manual test is a great idea, I'll try that this evening and see what I come up with.

Thanks for the feedback.

It was the seal/nut at the bottom of the flush valve. I took a large plumbers wrench to it to tighten it up some and the leak was gone.

Thanks for the idea of hand testing it, worked well.

Thanks for letting us know. Can't fix what you can't see right?