I winterized my old unit yesterday by parking the RV on a slope, and draining the water tank & opening the low water points. I also bypassed the water heater and drained it. Once the water was drained, I closed the tank drain & poured a gallon of fresh new pink stuff in the tank.
I went inside, turned on the pump, and got the line to the bathroom sink flowing pink when the pump started sputtering like it was all gone.
What?
Just air out of the remaining fixtures.
What gives?
I moved the unit back on the level to pour in the second gallon (never had to do that before), when I realized what happened to the first gallon...
Yep.
When I turned on the pump, it pumped it all right out of the low water points! My work area is gravel, so none of it flowed out; I knew what had happened after I moved the rig back to the level location..
So.. lesson learned - close off the low water drain valves BEFORE starting the pump!