Just thought I would throw my two cents in here. I installed this toilet and had a leak on the left tank bolt. I tried removing the tank and re-installing several times. I tried sanding the inside of the toilet around the hole and re-installing. I went so far as to alternate tightening the tank bolts a quarter turn each until they were tight. I tried over-tightening to the point where I was worried the tank would crack (thank goodness it didn't). Each time, it leaked. Finally, I used a coat of RTV silicone on the rubber washer that seals inside the tank. This fixed the leak. I'm not sure what else I could have done, but now the toilet is working great.