Gas drain back issue - possible bad pump, or ????

[mtnmankev]

86 GMC 2500 w/ 350, mechanical fuel pump.
Fuel filter before the regulator, and another (see through) between the regulator and carburetor.
Sitting overnight the gas drains back from the edelbrock 1405, and both gas filters have no gas in them.
Is it somehow draining back into the tank, or should I suspect a faulty fuel pump allowing it to go into the oil pan ?
I don't smell any gas from the oil on the dipstick, and the oil level doesn't change.
All hoses appear good and clamps are tight, no leaks to be found anywhere.
We have 20 minutes run time on this fresh engine and I don't want to ruin it with gas in the oil.

Edit: After running the engine (truck parked) 15 to 20 minutes, shut it off, look at the gas filters and they are empty .......
And we replaced the mechanical pump with another one that prior to this had no issues.

 

[AuroraGirl]

86 GMC 2500 w/ 350, mechanical fuel pump.
Fuel filter before the regulator, and another (see through) between the regulator and carburetor.
Sitting overnight the gas drains back from the edelbrock 1405, and both gas filters have no gas in them.
Is it somehow draining back into the tank, or should I suspect a faulty fuel pump allowing it to go into the oil pan ?
I don't smell any gas from the oil on the dipstick, and the oil level doesn't change.
All hoses appear good and clamps are tight, no leaks to be found anywhere.
We have 20 minutes run time on this fresh engine and I don't want to ruin it with gas in the oil.

Edit: After running the engine (truck parked) 15 to 20 minutes, shut it off, look at the gas filters and they are empty .......
And we replaced the mechanical pump with another one that prior to this had no issues.

i feel two filters is overkill generally unless you have a simple screen type as one of them?

Also, if the carb is good(I hear that high pressure or bad floats can let it seep past seals, which would flood your engine if you tried to start the next morning or something) then i would say pump. i know my pump is going out, similar boat. 1406 and no regulator, but im one of a few people who use a edelbrock without a regulator not facing any over-pressure issues, so i imagine i have a weak pump that is just right for the carb lol