You're going to need to get at the hose to take a peek at it. You should be able to open the lazarett hatch and stick your head in there. Maybe the hose is kinked or it's plugged up with debris. Just be careful you don't get stuck in that opening like I did. After that episode, I installed an 8" Beckson deck plate in the center of the inside transom and that was the smartest move I ever made. Not only was I able to get at the hose easier to replace it, but it gave me access to my gudgeons and my eclectic wire for my outboard charging system which I install in the spring and remove in the fall, along with my outboard. I discovered water stains under my lower gudgion after I was able to take a peek through the deck plate one day and I was able to remove both gudgeons, clean the area, re caulk them and reinstall both gudgions all by myself. So if you need to replace the hose, it's well worth installing a deck plate to get at it easier.
As for the hose; some guys use an "L" shaped rubber automotive hose for a replacement. I don't like rubber. I think that gasoline could eat it out if it stayed in that hose long enough but I may be wrong about that. My original cockpit self bailing hose met it's demise that way and I had a hard time getting rid of the gasoline smell in my cabin for many months of cleaning. I used a regular reinforced clear Vinyl hose with a nylon "L" connector and four stainless steel hose clamps. This stuff can be bought at Lowe's, Home Depot, or any hardware store.
Joe