My standard operation is to open all the stopcocks, drain the tank and all the lines and leave everything open. In addition I used to remove the annode rod from the hot water tank and drive around with it open to try to get the most water out.
Last year, I added vacuuming out the hot water tank with a shop vacuum. Basically take a piece of scrap clear tube (6-8"), insert it into the annode hole and hold the vacuum tip over the other end. You can see the water evacuating through the clear tube, so you know when you're done.
This is about twice the water I pulled out of the bottom of the tank this year, due to not setting the tank bypass before moving on and accidentally refilling the empty hot water tank:
After I was done I used the same clear tube and a funnel to add some good potato vodka to the hot water tank. I figure whatever is left will mix with the vodka and won't freeze.
So after the bypass to the hot water tank was set, I added a new winterizing step using this:
With the system open everywhere I hooked the garage compressor to my remote tank, and that to the city water inlet with the adaptor:
Then using the cut off on the remote tank, played with the pressure while going around the van and closing MOST of the system bit by bit:
Once I'd played around a bit, I found that a reading of about 22psi on the remote tank gauge, while actively airing the water system in the van, was about the right amount of pressure to push water without feeling like I was damaging anything.
With the pressure set I went around again and opened each stop cock or valve, and then closed off the previous one- I never closed the entire system, because I didn't want to pressurize it, just evacuate the water. As as side note, I took the shower head off so that I could use the shower knobs and not have to hold the shower head to keep it open.
I didn't seem to have a problem with the drain and vacuum last year, however there was definitely more water that the air adapter pushed out of my lines.
Normally I go back with vodka and put some in the main tank and then run a bit through the lines, however I ran out
after the hot water tank and will have to do this later.