After your boat gets craned in, and you've done the rounds checking for leaks, close the heat exchanger drain before starting the engine and motoring over to your berth.
When I flushed and refilled my coolant, I previously bought a cheap bilge pump and just allowed the coolant to run into the engine bilge, then pumped it out. Saved me hours of work: http://amzn.to/1eBW9BA