I do all three.
1) It's always cold after our last campout of the season so I open the hot and cold drains and open all faucets.
2) Later I envision low points in the plumbing and connect my blowout plug and open and then close each of the faucets when nothing but air is coming out.
3) Later still I start worrying about water remaineng in the pump so I connect the pump to the pink stuff and run enough to fill each of the traps.
4) Bonus - since the pink stuff in the lines is no longer useful, I open the low point drains again and collect the pink runout in a jug for next year. Also remove the filter housing and add that to my saved pink stuff. (being frugal, I probably saved a dollars worth of pink this way
Have a nice day - Darrel