Rear engine fuel drains

[wslade2]

very interesting

not to overthink this or mess with success....the end point for flow stoppage is the cutoff diaphragm in the flow divider. flow will come from increased pressure at the diaphragm above the set cutoff level pushing it open (the previously referenced 1 PSI). Pressure exerted at the cutoff diaphragm in the flow divider should be impartial to where it comes from: backflow through a check valve or forward flow through the system. Either way I would be suspicious of increased pressure in the system while at rest.

eg-probably check fuel tank vents to be sure they are clear and tank is not pressurizing from a blocked vent

I cleared my scupper drains (about same size as fuel vent) this summer due to water collection at fuel caps leading to water in my tanks. 10 days later an insect had made a nest in one of them again discovered via water collecting in one out of my 4 scuppers after a rain storm. It would likewise be easy for a tank vent to get plugged.