Having now lost a good number of connectors and plugs for my Suzuki 150, I’ve been looking at a few fittings on eBay which can be left in the flush port and connect directly to a hozelock fitting for when it’s time to flush through - so no connecting anything to the outboard each time (and less stuff going over the side…)
I’ve got a small Suzuki with same set up. I agree that having to change from one fitting to another is a bit tedious. I haven’t tried it, but wonder if a tight fitting plastic cap could befitted over the screw in metal flush fitting, with a small hole in it to allow the water to run as normal. I don’t know how much pressure there is in that water gallery, and whether it would pop out the cover, with consequential loss of water around the cylinder, though.
Perhaps it needs something more secure, which is screw on.
I’m sure someone here has a good idea!
Unfortunately, the marina hose at the dock is always left with just the bare hose end, so I would need a fitting to connect to the hose...... Perhaps easier to fit that end, without having to lean out over the engine. But yet another fitting to lose...
Apparently the "autostop" type connectors have a smaller internal bore on them which restricts water flow. I thought it was a low pressure supply but after removing the "autostop" connectors it flows fine.
Perhaps easier to fit that end, without having to lean out over the engine. But yet another fitting to lose... 
Eastern Thunder
Northern Exposure 5
