Before Y'all light your flame thrower, I'm aware of all the negative postings about using bleach... IMHO the information given is way overblown as I use bleach for many things to Kill bacteria and most viruses. Nothing else can (cheaply) accomplish that.
If I need to leave the tanks with 'dumps' in them, I use copious amounts of water and add bleach to the tank a cup at a time... Keep an eye (er nose) on it and if it starts to smell, add another cup of bleach.
I find it will not stink if you kill the odor causing bacteria and the solids will soften with the bleach water.. I also add water softener and Dawn liquid which helps soften and disperse any oily substance.
When I arrive at my next camping site with a dump station or any free dump station, Dump, rinse and add bleach, water softener and Dawn with a few gallons of water.
There is a long article on the web about this type of cleansing but I'm too lazy to look for it:
You may also see this:
PS to the posting that says he empties it on his 3 acres. Works for me, none of my family has the diseases that some said concerns them. Water and sunshine and worms take care of the effluent.
OK 'Flame On'