Everyone does itdifferent. Probably doesn't make much difference. After I drain my black and grey tank I close both valves. I dump enough pink stuff in my toilet to cover black tank valve then close toilet flush valve and pour enough in toilet to keep odors from coming up into MH. I pour enough pink stuff in the traps to make sure grey dump valve is covered. I don't want the valves to dry out. Since I blow out my lines pouring the pink stuff in is the last thing I do. On my MH and previous RVs the manuals say either method. Blow out lines or pink stuff. Whatever is more convenient. Since I may winterize more than once or twice in the winter I just blow the lines out.