Vacuuming out the water lines

It makes much more sense to have a compressor that you can use for inflating your rv tires and use for blowing out the water lines. I've always traveled with a compressor as I check tires and inflate as needed before hitting the road. All you have to do is make sure the compressor has the capacity to inflate your tires i.e. if your tires only inflate to 50 lb. psi, the compressor doesn't have to be as powerful as inflating motorhome tires to 95 lbs. psi.

sounds backwards to me.
bumpy

Cannot hook to the supply hose as it has a check valve. Would have to hook to both low point drains. You still need to drain the hot water tank and put antifreeze in the traps.

If you fashion an adapter to get a good seal, it should work. You really want high volume not high pressure to blow out (or suck out) the lines.

It shouldn't create enough of a pressure differential to damage anything as the water system is meant to run at 30-40psi.

Used to use a shop vac on our hot tub (as recommended by the manufacturer) worked fine.

I'm guessing you don;t have an air compressor?

You can TRY to vacuum out the water lines......except you will leave alot of water behind due to all the AIR you will be sucking. Open a faucet/suck air, open a shower/suck air, open the toilet valve/suck air, open a low point drain/suck air etc

Air flows easier then heavy water..
But hey....it's your RV go for it

No, not bright idea imo. What if you wanted or had to sanitize on the road. Extra space taken up with wet vac you would have to carry. Better off installing low point drains if you dont have any.
How powerful??? My 3 1/2 horsepower wet dry I can suck out radiator in car. About 3 PVC fittings reduced down to 3/8 vinyl hose. I have to remove my paper filter on mine.

I reverse the vacuum and let the positive pressure blow out the lines. YMMV.