Use Petroleum Certified Check Valves in order to Keep the running engine from sucking back through the other engine... So, you have a Single fuel line running into the Filter, then when you split the line after the filter, or if you have two outlets from the filter you put a Check Valve on each line with the flow directed to each individual Motor... That way the fuel cannot be drawn back... Basically your only allowing the fuel go in 1 direction (to the motor)... I would suggest putting a 1/4 turn valve or a Gate Valve on the "IN and OUT" of the Filter Housing in order to make changing filters hassle and messy free... I would also suggest to put your priming bulb in between your tank and your Filter. Then after the valved "Filter OUT" then split your lines with the check valves and then run your lines to the engines. If you need a drawing of this let me know...