Thanks all for the very helpful advice on fixing the crack in my black tank. I'm ready to fix, but was told I need to clean the tank very thoroughly and let it dry first. I'm permanently parked beside my house and can only dump into my septic system. Someone mentioned hydrogen peroxide would clean well, and then if diluted enough, wouldn't harm the septic. I also have some Thetford tissue digester and some Roebic K-570. What do folks recommend?