Cheryl, Genecop's instructions are correct from what I've read but we leave our drain line connected with all valves closed (normally). We also pour a small amount of anti-freeze into the tanks after draining them as we are in sub-freezing weather right now and I read on this forum this can keep the valve doors from freezing shut. We do have heated tanks.

Our camp host leaves his gray tank valve open but tells us that there is a chance of water freezing in the drain line. They feel since they are a family of 3 adults that hot water usages is sufficient to reduce those odds.

I do know that black tanks should NEVER be left open. That allows all liquid to drain away leaving the solid material to harden. Nasty!!!!! And I've read that the repair is not easy or cheap.

We empty as follows: Black tank is emptied first then a flush (I understand that not all RVs have this flush hookup), then empty gray tanks (we have 2) --- this rinses the drain hose. Close all valves and treat tanks. Hubby has even taught me how to do this. It's not difficult, just cold out there right now!