Gentlemen,
The no-start coach in this thread is a 2000 model with a C-12, so the first place to look at for suspected air in the fuel system is the primary fuel filter screen and/or it's O-rings. If the owner has not checked and/or serviced these O-rings, they could be leaking air into the system since they are now about 19 years old. The plastic screen column should be checked for cracks and/or fuel seepage at the O-rings at least yearly.
Mike,
The fuel return hose only operates under a few pounds of pressure at most. It only requires enough pressure to cause the return fuel to flow back to the tank through about a 3/8 inch opening, so there is virtually no restriction.
Gerald