Whatever you do, DO NOT leave the black tank opened all the time! When you use the black tank, use lots of water when you flush! Make sure you Toilet Paper is Septic/RV safe. We use Scott at home and in the MH as it is septic and RV safe. Try to dump when only when close to full IF possible. Gravity helps push everything out better. As far as cleaning, You can buy a wand to attach to a hose to rinse the tank after dumping. When we are going on a trip with full hook ups, I fill our black tank about 1/3 to 1/2 full before we leave to let water slosh whatever is in the tank loose from the last, and dump it as soon as we arrive. If you notice a smell, the make tank deodorizer things to help. We prefer the pods. We always drop two in the grey tank after every dump. The black tank sensor will typically NOT read correct after it fills up the first time for the trip due to "stuff" getting stuck on the sensors.
Grey tank is simple. Just the sinks and showers. Always drain this after the black tank to wash out the hose. You can leave the grey tank open if you like, but we do not. I have a fear of the smell running back into the RV if the traps are empty. DO NOT dump grease down your drains. They will clog your drain lines and tank just like at home.
As long as we have full hookups, we use out facilities as designed. If we do not, then the bathhouse tends to get used more. But don't be scared and not use them or flush toilet paper down them like some people may suggest.
