David Flew wrote:

Seems to me if the filters are clean and if there is a screen or coarse
filter to protect the pump the differences between having the fine filter
before or after the pump are probably academic. I don't know the pump
details or characteristics, but pumps need to have their inlet pressure
above some minimum figure - net positive suction head - or they don't work.
And it's much easier to find leaks of fuel out of a pipe than air leaks into
it. If it leaks fuel it's still working, if it leaks air in it probably
isn't.

So I'd think more about troubleshooting the system when there has been some
bad fuel and the filter pressure drop is getting high --- I'd like to see
the pump protected against things which might damage it, then a pressure
gauge , then the finest filters. It might not be the best arrangement in
terms of emulsifying water, but I'll bet it's the easiest one to diagnose.

Personally, I'd rather diagnose a leak in a vacuum system that stops the
engine due to air getting in the system than one in a pressure system
that keeps running but pumps fuel into the bilge until your tanks are
dry and then stops the engine. But that's just me.

Steve