Just did a quick drain/flush on our 21FSB the other day.I start by opening all the faucets,tank drain and low point drains,usually on the way to the dump station when we're leaving the CG,figuring that I'll get a lot more out heading up thru the CG than just letting it drain at the campsite while the TT is still level.
Hotwater heater bypass valves are under the entertainment center behind a panel.Pop the 4 screws,swing the 3 valves,open the access cover for the HWH on the outside,and remove the anode.I made up a 14" length of 1/2" copper pipe with the end folded over and about 20 holes drilled thru it on different angles.This slides into a piece of 5/8" hose with a female end on it(which I also use to fill my water tank) to flush the heater out,getting rid of the stuff that came off the anode during the season.
I use air pressure to push water out of the lines first,using an fitting that goes on the "city" water connection with a small compressor that runs off 12v dc and an air tank,filling the tank and then blowing the lines with no more than 20-25 lbs pressure.
Another panel under the stove will give you access to the water pump and there's a bypass valve and length of hose tucked up under there to draw nontox.Close the valve from the tank,open the bypass valve and start cracking faucets.I start at the galley and work my way aft,making sure to give the head a good shot of nontox also.
I dump about half a gallon of nontox into the tank,a splash into each drain to push the water out of the p traps and some into the head to keep the seal from drying out over the winter.
We live in Maine and by the middle of October freeze ups become a concern.We'll be using our 21FBS well into November and I've gotten this process down to about 45 minutes and will probably be doing it 2 more times before finally putting things to bed for the winter.
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