We have 3 tanks: Black for the toilet, grey for the shower and bathroom sink, grey for the kitchen sink.
Shower tank should never need anything. Every time you take a shower you're putting soap in the tank with water. Any bit of water left in the tank will slosh around and keep cleaning the tank. It should never smell either.
Toilet tank, well, that's another story.
Kitchen sink tank: As stated above, the kitchen sink is not a garbage disposal. Never put grease down it. Wipe everything with paper towel and toss the paper towel in the trash. When washing dishes, use a good grease cutter, like Dawn and it not only will wash the dishes, pots, and pans, but will also clean the holding tank. Occasionally use a little bleach in the kitchen sink to keep the drains from smelling, just like in your house, but flush the bleach on down so it won't cause any damage sitting. Bleach is damaging if it sits long enough. It's great from cleaning, but does need to be rinsed away.
If you do have "stuff" in your kitchen sink tank, then you should probably dump some enzyme drain cleaners down the drain and let it sit in the tank a few days. This will help digest and loosen anything that might be in there. Then drain the tank, fill again and dump it to flush it out real good. You may even take the camper on the road and let the contents in the tank slosh around and beat itself up in the tank before dumping. This will definitely loosen everything the enzyme eaters had for lunch.
Something like this:
Click here.Actually, Rid-X septic tank treatment is nothing but an enzyme - yiest mix, designed to digest solids. You could use it too, except it's a powder form and takes longer to work. Principle would still be the same. Flush it down the drain, let it sit a few days, take the camper for a nice bumpy ride, bring it home, dump the tanks, .... clean!
