im building a haynes roadster and have ajusted the back end to take a new alloy tank from a gbs car as its bigger (no baffles)
as im running fuel injection im going to add a sump to the bottom of my tank to stop fuel starvation to the fuel pump.
as far as i can tell its is a second small tank fitted to the bottom of the main one with the feed and return pipes fitted to it with a hole inbetween the two tanks.
how big does it need to be and what size hole do i need in the bottom of the orignal tank
i was going to make a open top box from alloy with the pipes fitted and tig it to the bottom of the tank after i have made a hole to feed it
i was thinking 1L and a 15mm ish hole will this be ok?

The sump on mine is pretty much what you describe. It's about 50mm deep and 150mm diameter cylinder (but a box will work as well). The inlet/hole between it and the main tank is about 50mm. 15mm would probably be too small as it need to be big enough that when going from a hard left to right turn the fuel passing from one end of the tank to the other floods it. My pick-up is in the bottom which is slightly better than the side and the return goes back into the sump. Never had the slightest hic-up, even running very low on track or in the Alps.

thats good to hear as i was worried i might still get a odd bubble of air now and then