I pulled the gas tank on the orange smasher and stopped up the lines up front. Each line is 15 to 18 inches long, so easily accessed.

I need to pull the rest of the fuel lines including the filter and pump (electric option is out - along with the wiring). How bad of an idea is pushing 50 lbs of air into the supply line and push out the gas via the return tube?

How much fuel is in there?

If you are talking about the lines that run from the tank to the pump to the engine and the return ... I would think a lot less than a pint. You could calculate it.

They will gravity drain nicely if you just disconnect at the pump and put a container underneath the open ends.

50 psi will just create a spray at the open ends. 2 - 5 psi would be sufficient.

OK, I guess I'll try a bike pump then. Why not?

Sounds good at 2-5 psi. Sounds like trouble at 50psi.