Home made one here. Plunger with a hose connection using brass fittings from Lowes or Home Depot. Level your boat, cut the plunger handle where the plunger will be partially compressed against the hull and turn the water on about 1/3 open. The water will pour out around the plunger until the engine starts and then you should she a small steam of water coming out of the plunger. In a minute you should see water coming out the exhaust.
I use the inlet of the vdrive. I bought a clear hose the same size as the inlet hose. I disconnect the inlet hose @ the vdrive and connect my new hose and use the existing hose clamp; put it in a cooler, turn on the water hose and you’re done. When the boat is warm I get my son to turn off the water hose and I just watch the cooler until it is almost empty then I cut the boat off. It makes picking up the cooler much easier when it is almost empty. I paid 5-10 bucks for the hose.