Hi,
Floe is a piece of kit to blow-down the water system.
I don’t think it will work because of the inboard water tank and the open-necked filler port.
We usually open all the drain taps (there could be 5 or more) and pull out the drain inside the tank. Open taps after turning off the 12v master switch.
We do this just before setting off home on our last trip so that the van movement shakes the last drips out. (Just be careful with the tank drain as you could get surface water or road grime pulled into the tank - a piece of paper towel or a cloth helps fill the hole.
Steve.
Ps didn’t you write a winterising thread Colin?