Toilet Tank Leak - Maybe a cracked tank?


DH and a friend replaced all the parts in our two toilets today due to slow leaks (both toilets had seals/gaskets/washers sooooo old that it was amazing we didn't have slow leaks any sooner).
Toilet #1 is fine. Toilet #2 is leaking from the tank (in the big gasket, screw mount area - we cannot tell for sure, even though we have monitored it very closely). While our friend thought the leak was coming through one of the screw holes, DH and I have think it's the big gasket seal in the center of the toilet (that seals the hole from toilet to bowl). The screw holes were replaced with the double rubber seals on the inside and the washers on the outside (as I have read in FAQ do-it-yourself toilet repair). So....everything looks good there....
We considered the possibility that maybe this gasket was not large/puffy enough for the hole, but it seemed to work fine for its twin in the other bathroom. Perhaps this gasket is defective?
We tried mounting and re-mounting the tank and each time we got different results (always a leak, but of varying degrees - from a very, very slow sweat, to a fast, fast drip - and then everything in between). Our friend attempted tightening the screws/bolts some more, but that had no affect. He didn't want to screw them too fit for fear of the tank cracking.
I have two theories:
1. The new gasket seal that goes from the outside of the tank to the bowl hole is not large or puffy enough - OR - is defective somehow (although it looks fine).
2. The tank has a hairline crack that we cannot see. I think we've disproved this theory due to different results with each mounting of the tank, but - I really don't know.
DH says, "Let's just call a plumber and be done with it". I am hovering around our drained tank at the moment feeling like I've just been defeated by it! I wanna fix that sucker myself!
Any ideas of something we should try differently, or should we just do what DH says and pay for the expert to fix up or mess?
Thanks! Paula
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Pokee wrote:

Also meant to mention, we drained all of the water and dried it with a hair dryer to inspect for cracks - we couldn't see any. We also did the best we could to make sure the 'inside' seal was sealed as well as it could be. It does look like it's fine.
I read somewhere else that buying an oversized gasket may fix the problem (maybe this toilet's hole is a tad bigger or misshapened?).
I've also read that we can try silicone on the seals? Of course, it has to be dry...
I think I just need more ideas of things to try before getting that nifty $200 bill from the plumber...
Thanks again! Paula
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Pokee wrote:

to tighten down the bolts more than I expected to in order to stop the big gasket leaking. I doubt you have a cracked tank -- once it cracked, I suspect it would probably split apart pretty easily.
But no guarantees your problem is like mine, and I've only done it once.
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Pokee wrote:

Yes to the last. You can buy a new wc for a good amount less than $200, and it would come with instructions on how to assemble the tank to the base.
Not saying it is not possible, but I doubt that the leak is from the big hole gasket unless you assembled it wrong, it doesn't fit you wc, or it looks damaged. More likely a seep from the two bolts that hold the tank on the base. The more times that you undo and redo the tank the less likely it will seal correctly. Some tanks require that there be a washer on each side of the tank bolt (bolt head, washer, and gasket in tank and gasket, washer, nut outside the tank, and then rubber gasket or sleeve(for protecting the base) and finally a washer and a nut on the under the lip of the base.
In any case, I would just buy new bushings (and probably the central gasket) and see if that works. There is very little water pressure on these seals (and none on the center when it isn't flushing) so the compression shouldn't need to be high if the seals fit well. Compression may be needed on the final nut, but is needed more to keep the tank steady than to prevent water leaks. Compression on the final nut may need to be higher for a WC that isn't designed for a nut between tank and the base.
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Pokee wrote:

You can buy a new tank? Not too expensive and no harder than doing what you have already done.
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I had one that the internal glazing was damaged, and it wicked water. I just covered the area with a thin layer of silicone seal, that was over 5 years ago, and it hasn't leaked a drop. I find that will even seal cracks, seems like the ideal material to seal with silicone seal, as it makes a long term repair.
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I had the same problem- very slow leak. I tried EVERYTHING, then replaced the toilet and the new one was fine. It must have been a very small crack in the old toilet. I would just go get a new one if I were you.
Eric in North TX wrote:

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fourempties wrote:

Well, we fixed the leak. We bought a HUGE gasket and put rubber washers on each side of the tank. Fixed. BUT....now we see a spot on the under side of the tank that is wicking/sweating water. When wiped away, I counted to 3 or 4 and then started seeing new beads of water appear in a perfect line. Soooo....there is a hairline crack - or the glazing was damaged (as Eric has reported). It is so slow - it would probably drop a bead of water every 12 hours - it's that slow. We'll try doing what Eric did - drain and dry the tank and seal it up and see what happens. Anyone know how much a new tank would be? It's an older toilet (20 years old), so one that size/color (beige) could be hard to find and expensive. Any thoughts?
Thanks! Paula
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