First things first. While you have the bedboard off, cut the last foot or so off, install a piano hinge and then install a brace below the unsupported edge. Then when you put the whole thing back, you will have a flip-up door for access to the pump. I agree, the original set-up is not, shall we say optimal for maintenance. If you have your owners manual, R-Vision say you only need to gravity drain and air out the system. I blow out the lines with a small plastic fitting screwed into the city water outlet. After draining, close the drains and faucets and then while pressurised with air, open one faucet or drain at a time till no more water comes out. Don't forget the water valve on the toilet and don't use high pressure. I use a small Black and Decker 110 Volt airpump, which is not capable of pumping much air, so I just hook it up and leave it on while I open the faucets and valves one at a time. I never have more than about 30 to 40 psi in the system, but it is enough to get the water out. I did that last year and added Pink Stuff to all my drains and to the holding tanks after draining the system. Don't forget to bypass the water heater and drain it as well, you will need to pull the drain plug from the outside for the water heater, it looks like it is a white plastic plug screwed into the lower side of the WH under the outside WH door area. While draining the lines, it is also good to open each faucet and allow air into the system through them which lets the water out through the low points. In my 251, there is a Main water tank drain in the passenger side rear compartment up against the rear wall. There are two more lowpoint drains inside the cupboards behind the large pots and pans drawer. Mine have pull rings on them and are easy to pull with a finger, just remember to close them before you use the system next. Of cours, we have fairly mild winters here and I am not afraid of a few drops of water which may be left in the lines. The antifreeze is good for the drains so the drain plumbing is not damaged, and I keep the rest of the gallon over the winter in the coach, so I can add some to the toilet if I need to flush it while I am there. Old men pee a lot, and it is handy to be able to use the Loo when I run the generator each month.