All my work was done with the fuel tank out. You might be able to do it with the tank in, but it would be tough. I really needed a good fix because I trailer on a very curvy and hilly road from the gas station to the lake. I need to fill the tank to the top at the station and not get to the lake house with gas all over the boat.
The first thing I did was install a conduit clamp
to the back side of the fuel fill and bought enough hose to run out of the tank vent, back through the conduit clamp and then through the guides under the deck and to the vent. The clamp is for about 2" conduit so it isn't tight on the hose. That didn't work.
I then bought probably 20' of hose, and a surge valve
. The surge valve needs to be on an angle upwards to work. I ran the hose out of the tank toward the port side, made a 12" full circle loop and then back towards the conduit clamp. I cut the hose just short of the clamp and put the valve in and then through the clamp and the deck guides to the vent. I have not had a leak since. I don't know if it was the loop or the valve, but it worked. I figure the fuel would have to have a lot of momentum to make it through the loop and then up to the valve.
The fuel vent line was expensive since it is supposed to be Coast Guard certified to be used in a boat. I may have paid close to $3 a foot. It was ridiculous.