This is the garden hose fitting brazed into the top of the sea strainer.
A hose attaches; the other end of the hose simply dunks into a 5-gallon bucket of RV antifreeze.
Close the seacock and run the engine until the pink stuff is gone. About a minute for me.
This is the same fitting with the cap in place. The piece of aluminum is to make it easy to open the strainer...
I flush the engines with fresh water every time they're run -- just by putting a garden hose in the sea strainer.
The fitting is only used to winterize the motors.
Both sea strainers. The red color is RV antifreeze.