I posted this explanation from a friend of mine who is a rubber chemist on another fuel hose thread. It's a bit complex, but it explains why we need the special hose.
The reason for the destruction of fuel hose in a submersible environment is that ordinary automotive fuel hose is a dual construction component. The outer veneer is made of less expensive NBR (Nitrile Butadiene Rubber), or CSM (chlorosulfonated polyethylene aka Hypalon), or ECO (epichlorohydrin). Depending upon the manufacturer the outer veneer could be any of these. The inner veneer is usually an FKM (fluorocarbon rubber aka Viton). There are several families of FKM that can be considered for use, each increasingly expensive in proportion to the chemical (fuel) resistance and ability to comply with EPA SHED (Sealed Housing Evaporative Determination) requirements. The outer veneer is low cost and designed to provide resistance to the underhood environment. The inner veneer (FKM) is designed for fuel resistance. If a dual component hose were completely immersed in fuel, the outer veneer would be immediately swollen and eventually destroyed. And if the inner veneer were made with less expensive dipolymer FKM it too could be swollen when in contact with the oxygenated (extended) fuels used today. The fuel oxygenates most commonly used are ethanol, methanol, or less common MTBE. Fuels that contain over 10% oxygenate extender are particularly aggressive. And increasing fuel extender increases the aggressiveness of the fuel. Some fuels can be 20% or more; avoid these. In order to achieve excellent fuel resistance for an immersible hose requires that it be made of FKM ($$) through and through. The best extended fuel resistant FKM's are the high fluorine terpolymer types ($$$). So the next time you spend an arm and a leg for a length of good immersible fuel hose you can thank your political representatives and legislators for passing stupid laws regarding poor performing crap extended fuels and creating the consequences (fuel hose and seal problems) that they don't understand.