I used a creative method in my 35. My tank was leaking and getting it out requires major boat surgery or pull the motor, or try to cut the tank in half inside the boat. Instead I installed a 7 gallon tank in the locker where the water heater is located. The tank fit nicely all the way in the back directly under the fill fitting. A few lengths of hose and some fittings and clamps and back in business. I can still get down in the locker to work on stuff like exhaust system or stuffing box. Next time I pull the engine I will replace the original tank, meanwhile I have to fill up more often from jerry jugs.
If you are intent on replacing the tube, you could maybe run a pickup tube from a portable tank or use a section of fuel hose down the inside of the pickup tube and then you'll need some way to seal it at the top, maybe a custom made fitting to screw in with a barb on the inside for the fuel hose in the pickup tube then screw that to the top of the tank and a barbed fitting to run the hose to the pump? A good machinist could make something pretty easily I would guess. Then you could easily replace the hose periodically. On that subject while installing the small tank I found a lot of my hoses were rotted out and I replaced the whole mess. You can get the electric pumps at NAPA auto stores if you are looking. A lot cheaper than marine places. Also hardware stores and auto parts stores often stock fuel line also a lot cheaper than marine stores. My local NAPA store had fuel line rated for diesel. Your pickup line does not need to be very large, our engines sip fuel so the flow rate is really low. I've always thought 30 gallons was too big a tank as I rarely use that in a whole season. If I end up replacing mine I will make it a lot shorter and maybe 20 gallons so the fuel doesn't get stale and maybe I can get access for a cleanout port.
