How to fix my leaking toilet tanks?
This might sound strange but sometimes people inadvertently lean against the tank while sitting on the toilet seat.   This can put pressure on the large gasket that is meant to seal the tank to the toilet.  Even a new gasket can be compressed on the back side near the wall of the ring gasket which could cause leaks on the front side of the gasket. In the beginning of this happening, the leak may stop once a person stands up but eventually the rubber gasket can deteriorate and lose its sealing ability. A possible  fix is to avoid leaning back against the tank. Depending on the gasket, it might have to be replaced if it has been damaged from compression. Another preventative solution is to put a proper size board or  other solid material that fits the space between the top, back side of the tank just below the lid and attach it to the wall so that if someone leans back, the block of wood can help prevent tank from leaning. Nash Stephens