I have a Merc 4hp Saildrive that I use as my aux.
The hose flushing attachment fits into the bottom of the engine casing, you take out a small threaded plug and screw in the hose attachment which has the same thread. Mine has a short tail of hosepipe and a normal hose connector that I then fit onto the garden hose.
Unfortunately over a number of years of use taking the plug out and fitting the adaptor, the threads have badly worn on the engine side (guessing it is probably just aluminium), and it now barely grips. Apart from worrying about the plug popping out and losing cooling water, it means I dare not remove it again to flush the engine, and I don't want to have to set up a tank each time as it is a pain.
I am pretty sure a helicoil type thread repair won't work as the engine obviously has a cavity on the inside and helicoils are not really designed for that. There's also dissimilar metal corrosion to think about with a stainless helicoil against whatever the engine casing is, plus hot salt water!
My other thought is to try and find a thread adaptor and drill it through, drilling out the engine port and tapping it to the next size up (e.g. M8 to M10), fit the adaptor in with loctite and then just screw the blanking plug or the flushing adaptor into the thread adaptor.
This sort of thing https://www.jpldirect.co.uk/catalog/...rs_E30400.html
Before I order some (nothing like that available locally) I wondered if anybody might have other ideas that I hadn't thought of, or had come up with a solution to the same problem in the past?