im trying to check my fuel line for air but cant find the bleeder valve

 

There isn't a Schrader valve on the later build 7.3's SD.. It's a 'return to tank' system.. Although there is a fuel filter/water seperator drain, and a plug in the canister/forward to install a test gauge, and a 1/8 pipe plug at the end of the cylinder heads to test pressure/volume..

Whats the concern for air in fuel?