There are many kinds, so there is little different for everyone.
The problem is that 胶皮塞 and what it sits on. They both have to be right for it to work. Sometime is the seating gasket has the problem. Their surface has to be clean and position should be right.
One more thing, for some toilet 胶皮塞 is like a ball, it should be filled with water , there is a little tub goes into it to fill the water. I have this kind. One of them have some leak. I adjust water level of the toilent (bend that metal bar) to make tank water level little lower than the 胶皮塞 water level. a little pressure expand the 胶皮塞, make it seal better.
And the design of the toilet , couldn't 100 percent leak proof, If you lose half tank of water per 24 hours, it is not that bad.
