If you’re wondering whether you should leave your RV’s black tank valve open or closed, the short answer is: Closed. You should keep it closed until the tank is ½ to ⅞” full, or you’re getting back on the road after camping. Best not to travel with a full holding tank if you can help it. They’ve been known to fall off! 

When it comes time to dump, ensure your camper is parked on a level surface. Attach your 3” sewer hose (aka “stinky slinky”) to the fullway valve outlet (bayonet fittings are the most popular), then drain the tank all the way. Avoid sags in the drain line. Dump the black tank first, then gray, if you can.

Next, rinse and flush the black tank with 3-5 gallons of water using an aftermarket toilet tank wand (aka “swivel stick”) or built-in black tank rinse, if your RV came so equipped. Check the color of the effluent through a clear sewer hose elbow in your drain line. After those few gallons, the water should run clear. Once that happens, close the sewer valve.