You *have* replicated my system because I also "T" the transfer pump into the EFI return line to feed tank.   It has no problem transferring fuel with this arrangement.  Facet makes these pumps in several different pressure ranges.  I think mine is the 4-6 psi model.   I used 3/8" line in this portion of system.  Did you use something smaller?  Hi Tracy,
 
That's interesting, because I didn't recall that you Teed yours also.  One difference I know we've discussed is the fact that you were smart enough to run your return line to the top outboard end of the tank, so it wouldn't be submerged.  Mine is just a fitting on the removable cover where the fuel level sender is.  That causes me some problems with the fuel wanting to seek a common level between tanks when it's more than about half full, but I doubt it's the return problem.   I believe my pump is a 4-6 psi version, but I'd have to look to be sure.  The whole fuel system is AN-6 (3/8") line, with the exception of the tank vents, which are AN-4 I believe.   I also connect my transfer pump near the top of the fuselage, so the facet has to push the fuel a couple feet uphill, to where it meets the return line.  Perhaps that, and the one way check valve I just installed are just too much for it.  What I need is a pump the same size as what I have, but in about 10-15 psi.  Seems like I looked, but couldn't find any such animal.   Thanks,
Rusty (off to remove the VW engine from the Sonerai... long story, but I still have two unflyable planes)