winterizeing

I live in Minnesota and I fill and drain water several times a year due to our temp fluctuations in spring and fall. I have never filled the system with RV antifreeze even to 30 below. I open the fresh water tank and line drains, open all faucets to let air in, pull the anode out of the water heater and wait to run dry. Then I cycle the pump some to get some air in it and step on the water fill pedal of the toilet. Then I put some RV antifreeze in all traps, both kitchen drains, bathroom sink and the shower/tub. I put plenty in so that any water left in the drained grey water tank gets some. Then I pour a fair amount down the toilet hole so that any liquid left in the black water tank gets some. It doesn't matter if some water is left as long as there is air for it to expand into. I have never had a problem.