Bob:
That line to your fresh waster system was likely to flush the
engine for
storage. Not a bad idea essentially, but flawed in it's execution.
In my opinion, you should remove that interconnect.
Plug the T on the fresh
water side. Put a pipe
plug on the
salt side near the ball valve.
When you want to flush the
engine, pull the plug at the ball valve, install a length of hose and put it's open end in a bucket of
water. Close the through-hull, open the ball valve and run the engine, keeping the bucket near full, The engine will suck from the bucket nicely.
Never feed pressurized water to the engine. Pressurized water has no problem getting past the flexible impeller lobes.