I have a commode in my home which the tank tops off about every 30 minutes or so. It doesn't run water very long, but is annoying. This commode has a vertical plunger which seals against a rubber seal at the bottom outlet of the tank. The plunger is activated by the flush handle on the exterior of the tank.I have cleaned the tank around the seal, replaced the rubber seal and plunger, but the problem stills exists. I would appreciate any suggestions. Thanks