Here is my antifreeze recirculating contraption.
This enables you to run your engine as long as you need to.
Thermostat open in other words.
This is to make sure the antifreeze is completely mixed throughout your boat's entire cooling/heating system.
You can also use it to recycle & re-use your anti-freeze - IF you have an overwhelming & burning desire to go out and freeze your butt off for a New Years' Day Ski @ 20 deg. F - as some crazy Adirondackers have been known to do....
The key to it is to have a one-way valve. So that the hose going to the raw water pump stays full.
This will cause less wear & tear on your pump's impeller.