Okay... .Time for the "Crappy" tip (Pun intended).
Bring gloves... Rubber or similar preferred. Even the cleanest of black/grey water drain systems can still get messy. It's always nice to have a pair of gloves appropriate for connecting/disconnecting the hoses and what not. Even in the end, still wash your hands.
Also, if you are hooked up to sewer, it is NOT a good idea to leave the drains open, particularly for the "Black" water. Sewer gas can come back up into the tanks if you do. The grey water is not as bad to leave open as most grey water drains have a "Trap" to keep out the gases, but the toilet is usually just a valve (or double valve) that opens up to drop the waste into the tank.
When at the fort, because my DW and DD's can't take brief "Camping" showers, our Grey tank fills up quickly. (in 1 day, easily), so I leave the grey water drain open. When it's time to empty the "Black" water tank, I close the Grey water tank in the morning (at least until the showers are done), then I empty the BLACK water tank (solo). Once it's done, I then close the black water tank valve and follow by opening the grey water to flush the hose clean.
Next important tip. NEVER EVER use the green hose. Okay, I know you may have used the green hose to drink out of at home when you were a kid, but here.... The green hoses at the fort may also have been used to flush the sewer hoses or worse. ALWAYS use a Potable Water (typically white) hose for your clean/potable water needs. I also use a filter on my line as well.