I had a toilet tank that needed a new flush valve, so I picked one up at Lowes, a universal plumb pak....no matter what I did, everytime I put the tank back on, a small leak happened around the nut of the flush valve on the bottom of the tank. I even filled it at the kitchen sink and watched to see if it would leak, but when installed, a few hours later it was leaking on the floor. I had another tank just like the first and put a new flush valve on it and lo and behold, a few hours later, it leaked also...for the life of me I really don't know what I was doing wrong. These were toilets in a mobile home...a 'oso' model(?) Don't know if I was tightening the nut too tight or didn't have it tight enough...any thoughts? I finally purchased a new tank and put it on, no problems, as of right now.
BTW...on the tank to bowl gasket, does the gasket have to fit over the threads and the nut? or just the threads only? thanks, Mike