I can't get the picture to post at a reasonable size so I'll just ask the question. I'm looking at our fresh water, water pump with the motor in the rear. There is a thumb tightened line coming into...
Look for a tee in the water line coming from the fresh water yank and the water pump. This will have a select valve installed. The line connected to this valve is short and not connected to anything just laying on the floor and will probably a stopper in the end of it.
This is the line that goes down inside the pink stuff container...
Should look something like this google photo
See if you got something like this around your water pump area...