Sump and plumbing questions

[TBSB2019]

I am running 3 dc pumps on 3 tanks. Varios 6 on a 60 gal. (Overpowered) Varios 8 on a 180 gal. (Overpowered) and a Varios 10 on a 250 gal. (Way overpowered) You only need a pump that can push enough for the amount of turnover you need. My 250, I am running about 1200 gallons an hour (300 through UV and 900 through tank which is almost 4x turnover for the tank). People that run AC pumps use a valve on the return line to control flow where the DC uses a controller. But in both cases, for sound from the overflow, you need a valve to keep one overflow line at full siphon, a slight trickle in the secondary, and if you have a third (which I do on two tanks) is for emergency. The valve in the overflow has nothing to do with flow control. It is only for overflow noise.