Hey Jasbo, welcome to the forum. Lots of good information here.
Do you know which tank is leaking? I assume you have more than one. You did not say what model floor plan you have.
It sounds like you may have something stuck in the valve preventing it from closing all the way.
If it is the black tank, only drain it when there is a lot of water in it. Use plenty of water when flushing. And always use the rinser.
You might have to let it all drain out and then take the valve apart. I had to do that on a black tank valve a long time ago.
My wife no longer uses a half roll of TP at a time.
Let us know what you find.
Peace
Dave