many folks pump directly into their growbeds, using pumps on a timer, say 15 minutes on and 45 off. i have a "flood tank" based on the barrelponics manual, and my pump is running 24/7. i think you first need to determine how much water it takes to flood your growbed, how deep is your growbed? what will you use for media?

regarding drains, i hear great things about the afnan siphon, takes a little work to adjust from what i understand, but very reliable. will you have one large bed with multiple drains/? or multiple beds draining into a header or something that drains into the tanks?

i have 3 55 gallon tanks on the floor, with one growbed draining into each of the "outside" tanks, with the pump in the middle tank. i'm using a no-holes-overflow between the two pairs of tanks

details man, we need details!