Maybe it is time for a "process check".

The original purpose of this thread was to create a better fuel pump, fuel pick-up & return installation. I, as the instigator, hate the current method. The preferred method keeps the cost reasonable (we all know that we can do anything with sufficient funds).

There has been good discussion on how the GM sumps work. The question discussed is if the GM unit's fluid level can be above the tank level. This discussion is pertinent to the original purpose since it relates to internal components and operation.

I think the consensus is that the GM unit can have a higher fuel level than the tank. If so, the discussion can go back to how we can secure it to the top of the tank and what components to use. A couple alternatives for securing to the top have been discussed (notably casting a thread and lock ring and re-purposing the existing boot).

If there is uncertainty relative to the GM sump level being above the tank fuel level, try this mind game...

The unit is plumbed so that 100% of the fuel returns to the sump. Will the sump be higher than the tank? A: Yes ( I presume we all agree here)

As above except we divert some percentage of fluid flow from going into the sump. Will the level in the sump be higher than the tank? A: Depends and is a function of inflow rates through the backflow valves and the percentage returned.

So let the discussion go on ........................

Nick