Toilet tank bolts (getting them watertight)

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Well-Known Member
May 15, 2008
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I've got toilets that have 3 bolts for the tank. I think this is an older design. The bolts don't have a washer or nut between the tank and the base. There is only the one nut, so the base and the tank are squeezed together by the same force holding the bolt against the rubber washer inside the tank. I'm afraid to really crank on these nuts because well, no one wants to crack porcelain. But I'm having trouble getting them watertight.
What should I do?
1. Crank on those nuts harder
2. Apply some silicone caulk to the washer before putting it in.
3. Something else?

Are the rubber washers new ?
If not, get new washers. The old washers will take a set over time.
I had one like that and I don't know if it was correct or not but I dried it all out and smeared some sealant on the rubber ring and it worked. Can't remember what I used as it was whatever I had around.
gfw, you can usually add more nuts & washers. You can put a washer on either side and get more nuts to secure it (which is what I did). I also recommend wing nuts for the very bottom as they are easier to turn. I got a bolt kit from Lowes that has large rubber washers and some wing nuts. You never want to try to over-tighten.
This is the kit I got from Lowes

I got wing nuts separately.
Add more nuts and washers.

From the top (inside the tank it should go like this: Bolt head, rubber washer, tank bottom, metal washer, nut, shim, bowl rear mount, metal washer, rubber washer, wing nut.

Tighten (not tremendously tight) the first nut (which ends up between the tank and the bowl) before putting the tank on the bowl.

The middle nut must not touch the bowl porcelain; use shims if needed s little to one side or the other to hold the tank a little higher off of the bowl rear.

The middle nut makes it easier to seal the bolt to the bottom of the tank with less tension.

Without the middle nut the bolt shank and the bottom nut have to exert enough tension to hold the top of the bolt sealed and this puts more tension on the bowl porcelain in back.
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Update. It seems the original installer, 25 years ago, didn't use rubber washers at all! What I thought was a badly decomposing and bleached washer was in fact ... a donut of plumber's putty. Anyway, that suggested the solution to me. The trouble is irregularities in the shape of the tank surface around the hole that a rubber washer doesn't quite deform enough for. So I added a (smaller than the original!) donut of plumber's putty under the washer to squeeze into the hole, the threads, etc. This concept was blessed by the guys at Home Depot and It seems to be good so far. Obviously I'll watch it for a while.

zannej & ajaynejr - I now believe I could add the middle washer and nut. I previously thought this toilet just didn't have enough room for them at all, but looking carefully, I think they'd just fit. If I have any further issue, I'll do that. Thanks!
Steve123 - the old "washer" had indeed taken quite a set, since it was actually putty that had hardened in the shape of the hole. :)
To summarize ajaynejr, you want to install a system of rubber washers, metal washers, and nuts, which makes the critical seal of the tank bolts totally independent of the tank to bowl connections.

So that you could carry the tank in your hands, full of water, and it would not leak past the bolts.

With the bolts just providing a strong mechanical connection of the tank to the bowl.
Jeff, understood. Up until now, I had thought that with these particular 25y old Mansfield toilets there wasn't enough room for a washer and bolt between the tank and the base. But now I think they'd just fit. So going forward I will probably add those. (I won't mess with the ones that are already working though.) It's clearly the superior approach to getting a watertight seal. The only drawback I can see is that one will have to be more careful lifting the tank off and putting it back on so one doesn't strike the base with a protruding bolt. But that's not a big deal.
I did the same on all 3 of my toilets (they were all over 25 years old at the time). Emptied tank, cleaned all around all openings, replaced the bolts a three turns beyond "finger tight", and havent had any leaks. The original washers had gotten brittle and misshapen over time.
Cleaning is a step I forgot to mention. That is a very good idea. Keeps grime from being under the washer if you clean thoroughly before putting new ones in.