Fuel Tank Bulkhead fittings

[claycookiemonster]

Just where do those 1/8" thick washers go when installing the vent and fuel line fittings to the inner rib of the tank? I got enough to put one inside and one outside on each fitting, but the plans are pretty unclear. Also, though my current engine thought (Mattituck TMX) doesn't require a return line, some guys are installing one "Just in case." If I determine later that a return line is needed, MUST it return to the tank? Can't it return to another point in the fuel line eliminating the need to punch another hole in the tank?
Clay Cook
Pro-Seal Arrived, time to get dirty!

[airguy]

Yes it could - but keep in mind thermal considerations. If you have a fuel system that pulls fuel forward of the firewall and then sends some of it back (as some FI installations do), that fuel picks up heat on each trip through the firewall. You will be recirculating a good portion of the total fuel flow, potentially resulting in some rather high fuel temps, especially during low-power operations (such as descent to landing) which could produce vapor-lock at a most inopportune time (such as go around). Dumping the heated return fuel into the tank away from the fuel pickup will lessen this risk.