Digest-it was recommended to us by a fellow camper. It is difficult to find, though. But I was told we should put it in the black tank and in the gray as well to break down grease.
Also, I was told that if you hook up to sewer and leave gray valve open, the grease will coat the bottom of the tank and create problems. Not sure about that piece of advise, though. Seems the grease would either coat the bottom or coat the sides a la bath tub ring. If you put the enzyme type treatment in there with a little gray water and travel with it for a while, the enzyme will get stirred around evenly, or at least will swim around to all parts of the tank submerged in the water and eat away at whatever is in there. I generally try to leave a few gallons in the gray tank for this purpose and to keep the seals from drying out.
