Fuel lines

Where does the return line go at the engine side of things?

Very simple. You put this inline fuel filter in it and plumb the return line to the 1/4" nipple. That nipple has a metered orifice that only allows enough return so as not to drop fuel pressure too low.

https://www.oreillyauto.com/detail/...ickup-rwd?q=fuel+filter/water+separator&pos=1