There is lots of on going research on that subject. People have used chlorine, hydrogen peroxide (food grade only), plain water (or spring water) and many other things. The last 2 years I've just run the vacuum until the inside was dry and then cap it tight. On a small system without vacuum you'd be hard pressed to get the lines dry. Using any chlorine leaves a salt residue that attracts squirrels. I guess I'm saying, drain as best you can and leave it capped. Then if you want, push some clean hot water thru it just before things freeze in the fall and drain it well.
Dave Klish, I recently bought a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.