You will need a stinky slinky, aka sewer hose, to dump your black and gray tanks. Treat these carefully so they don’t leak, and treat them as if they are covered in poop… Because they are. Yes you should rinse them out, but don’t stick a hose in them, and don’t put them on the picnic table to dry out.
Black tank means poop tank. Gray tank means anything except poop and pee. Fresh tank is clean potable water.
You should dump your black and gray tanks when they get full. For many that’s about once a week for black, and the gray more often.
****Your black tank sensors are never going to be accurate, just ignore them.
****Do not leave your black tank valve open.
Always dump the black tank first, then rinse it, then the gray.
Use a Blaster to rinse your RV tank. Be sure it has a backflow protection valve.
Fresh water tank should be sanitized at least yearly