JCO: Currently the drain is a capital M with the drain coming out the middle leg of the M and the two longer legs nearly touching the bottom. It's not possible to make it a U and connect to the discharge line. In the pictures you should be able to see that each barrel has it's own ball valve. I have kicked this around in my head all day.
***update***Okay JCO, I reread what you wrote and this makes better sense now. I will build ONE barrel your way, and see if it works. Then copy to the rest if it does. Too expense to build them all without testing...LOL.

And there's only two ways to fix this if I am right. 1) reduce the valves down to reduce flow to barrels. Each one will have to be adjusted manually and will be different. This will prolong the cycle of each barrel to nearly 15-20 minutes or more per barrel.

Or 2) Enlarge the discharge lines to 1" and a 3" graded line to carry to sump. This is going to SUCK as I just bought all the damn PVC and lines which was over $100 in 3/4" and 2". I don't even want to know what it will cost in 1" and 3" and fittings.

IF I am right, with either of the above solutions I will let you all know.

IF the cycle times end up being further apart, than I just have to adjust what I grow I guess.