Toilet won't stop leaking after replacing all gaskets
Ok, I consider myself a fairly competent do-it-yourselfer. I've replaced wax rings, flappers, and fill valves before. So, I know my way around a toilet. This problem has got me utterly baffled. I have a vintage 70s blue American Standard toilet. A few months ago, the tank started leaking into the bowl. I could see a faint stream of water in the bowl and could see the water level in the back of the tank slowly drop. The float would drop enough and refill the tank... slowly drain again. Repeat. My first thought was the flapper. I replaced it and it continued to leak. I tried 2 more. No luck. I verified that there were no exterior leaks- I did not feel any condensation or water around the tank bolts underneath, and there is no water on the floor or by the toilet seat bolts. So it must be one or both of the tank-to-bowl gaskets. I didn't have time to fix it, so I tried just cramming a bunch of plumbers putty at the bottom of the tank around the gasket. It didn't help. So, I went and bought a complete repair kit. I replaced both rubber washers and tank bolts, installed a whole new overflow pipe assembly (the guy at the store said it could possibly be cracked), complete with 2 new tank gaskets. The toilet still leaks. I took the tank off again and even added some silicone around the toilet base before I put the tank with gasket back on. It still leaks. What am I missing? There's no obvious cracks in the tank and I don't believe there are any cracks in the toilet bowl. How can this still leak? I'm baffled and frustrated. This isn't rocket science- toilets are fairly straight forward. There's only so many ways a toilet can drain. What would cause the toilet to still leak like this? A few people online said that if the tube from the fill valve is too long and goes too far down the overflow pipe, that this could cause a siphoning effect. I don't understand how that even makes sense. If the tube is down the overflow pipe, how can the it siphon water out of the tank when the water level is below the rim of the overflow pipe..? Can anyone offer any HELPFUL advise?