I bought the FluidMaster toiler repair kit and replaced all my toilets in the house. 2 of them are okay but two are leaking a drop once in a while through the bolt. I did follow the bolt installation instructions. Also tried to tighten it more but no luck. Any idea how to fix this? Is there anything that I need to apply on top of the bolts (inside the tank) to make it waterproof?

Did you place the washers as instructed? (see image)
Also be advised that if you tighten the tank bolts down tight that the first time some one leans back it will put a strain on the floor of the tank and crack the porcelain. ( If that hasn't already happened.)
The tank should have a 1/4" inch of play. Snug the bolts next to the tank tight and when you set the tank on the bowl leave a little play. Good luck, Tom

Thanks for the answer. Yes the assembly was done correctly. As I mentioned two of the 4 toilets have no issue. Only 2 of them leaking through one bolt.Do you think adding double rubber washer will fix the problem? Or may be adding some silicon will fix the leak?

If you've cranked those bolts down real tight check around the holes for hairline cracks, Toilet tanks MUST have 1/4" of play. Let me know what you find. Cheers, Tom

Looks like the gasket was not fitting properly on the valve. So I replaced that. Water seems to be stopped now.
For other tank I noticed lots of glue. So looks like the earlier owner might have repaired it. I will replace the tank. It is universal rundle 4471 toilet and I called 3-4 local plumbing stores but nobody has the parts. They told me UR is out of business. May be I need to replace the whole toilet I guess.

My experience is that you have to torque the tank bolts a lot more than you imagine! And! Although some "snobbery" seems to exist, I had to use lots and lots of silicone sealant on one tank bolt. The rule of Do-It-Yourself is Do Whatever Works! Sometimes you get a toilet that is a half-hour install from box to floor and sometimes you get a toilet repair that takes days and days of tinkering to make it work! Just use rubber washers next to the porcelain and you should be okay. Don't be a snob! Use silicone sealant if you have to--it will peel off should you ever have to remove the tank bolts again.

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Originally Posted by hikpd

Thanks for the answer. Yes the assembly was done correctly. As I mentioned two of the 4 toilets have no issue. Only 2 of them leaking through one bolt.Do you think adding double rubber washer will fix the problem? Or may be adding some silicon will fix the leak?

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Try liberally applying silicone sealant on both sides of the rubber washer inside the toilet tank. Also, it is not a crime to use a metal washer on top of the rubber washer inside the toilet. The idea is that the metal on top of the rubber will compress when the nut is tightened on the outside. Just be certain to have rubber next to the tank, inside and out, always. You should be fine. Apply the silicone as you would if you were buttering a piece of toast. Never mind the people who say you should not use silicone. It will peel off if you ever have to take the toilet tank off again. No problem. This is what worked for me as well as tightening the toilet tank nuts much more than you would imagine. And no, I did not crack the tank. C'mon, people. Toilet tanks are not bone china!

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Although some "snobbery" seems to exist, Don't be a snob!

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Could you
Please explain that remark?

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My experience is that you have to torque the tank bolts a lot more than you imagine!

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And it's been my experience that if you crank the tank bolts down too tight , so there's no "give" that the first time someone leans back against the tank that the china will crack around the bolt holes.

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C'mon, people. Toilet tanks are not bone china!

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As a matter od fact toilet tanks ARE made if china. Regards, Tom