On my OFF-ROAD POPUP trailer I never did want to use the pink stuff inside the water tank. I just drained all of the water I could from the low drain point with both HOT and COLD spigots opened up when draining. It doesn't get all the water our of the hot water heater for me but i suspect just a small inch of water or so in the very bottom of the water out-flow pipe fitting... Should be plenty of room inside the tank to expand when freezing. I also pop open the hot water relief vale on top of the water heater when I do this... This also helps draining all of the water out using the low drain point.
My water system is small so I only use the blow-out method and only add the pink stuff to the two P traps I have. I also drain my one and only fresh water tank too... Everything else is either drained through the low drain port or blowned out down the sink using compressed air at the city water port. I use one of those 12V TANKLESS portable compressors which is slow building up pressure and I can hook it up and walk inside and open the values etc...
The beauty for me is we like to camp anytime Summer, Fall, or winter and using the blow out method is best for us to use. Just add fresh water the next and we are back in water business again... Only takes a few minutes to drain everything and then use the 12V small tankless compressor to blow out the lines...
Roy Ken