1-1/4" I believe.
Old boat had a tee with a garden hose thread on it. just screw in the hose and go on a DD if the connection is on a horizontal part of the hose after the trans cooler. Or close the r/w valve on the hull if you're losing water out the intake.
PO had a quick connect garden hose fitting that I used most of the time. Allowed you to put one end of the quick connect on the T fitting and the other on the hose so you could have the water turned on to the hose and not get water everwhere. Just sanp the quick coupler in and start the engine.
'06 X2 MCX
"I understand why some people may not want to do this the way I have recommended but I can't understand the death grip some people have on a toilet plunger with a hose fitting." -JimN