Does anyone know what the 3/4 turn ball valve located on the port side at the water line (behind the fresh water tank) is for? The line from the valve goes to the flush valve at the strainer and leaks water after I flush the engines, even though the valve is closed.

some of the 35's are rig with 2 strainers some with 1 not sure which valve you are looking at can you post picture

Single strainer, line goes from flush valve to ball valve mounted on thru hull fitting behind fresh water tank at water line.

On my boat I was told it was a pressure relief overboard dump. In my application it proved to be problematic when on plane as the through hull would suck air back into the strainer causing low water pressure. So I have the valve at the through hull closed. But, I wouldn't recommend this unless you experience the same issue. Too much water pressure can be problematic too, so you would need the valve open.

And, yes, they drip water when the valve is open.

Makes sense - thanks for the response.