In my post i was actually refering to a suction line, and pump it out with a transfer pump. 3/8's should make a decent flow, when pressurized. We use oil transfer pumps at work to drain down large drain pans after oil changes, to fill our waste tank.. little 12v job.. seems like it was about 160 dollars.
I would also think that if you were feeding of the bottom like that that it would be very prudent to put in a water drain petcock, and also a bypassable spin on style fuel filter in line with the transfer pump.
Course.. using this method you could simply syphon from a top hole as well.
I agree gravity feed would have a head limited / dependent on the volume of the tank.. etc.
Soundguy