Here's what I do. Empty the FW tanks
. In the FW system disconnect the in and out of the hot water tank and join them together. Drain the hot water tank into the bilge. Pour the pink stuff in the FW tank. Run it through the system. Open all the taps and run till nothing comes out. Leave the taps open. One gallon of pink stuff should be plenty. If you don't bypass the hot water tank you'll need gallons so bypass the hot water tank. That's it for the FW system. The shower
pump is in this system so open that too. If it's the shower drain you're worried about pour some pink stuff through and pump.
Pump the head dry. Pump out the holding tank. I pour a bit of AF in the head just to make sure. Pump it into the tank.
The bilge pump I've never worried about because the bilge is dry. If you're concerned pour some pink stuff in the bilge once the boat's on the hard
and pump it through. It doesn't hurt to leave some AF (the pink stuff) in the bilge.
Don't forget the fridge drain. The engine
is a whole different story. We're here in the great white north and I don't know where you are. Our boats are on the hard
in winter, most of the spring too.