Originally Posted by jim1521 I use Walex Porta-Paks in the tank. The other thing I do is what I call a "Deep Clean". I dump the black tank as normal, then add a VERY large squirt of Dawn into the tank; I mean about 1/2 of a small bottle. I then proceed to fill the black tank to as close to full with the fresh water internal rinse system, leaving the dump valve closed. When I've got it nearly full I'll let it sit for about an hour to work on cleaning the walks inside the tank. I then proceed to dump the tank, ...