so I've always based my 1" drains off of 700gph but I've also heard they are capable of 1000gph. I'm honestly questioning that it may be more at this moment because I am currently running a jebao 18000L (5000gph roughly) in my setup plumbed with a return of 1.5 that splits to twin 3/4 in the DT. Its a 7ft return made out of smooth wall flex hose with 2 gradual 90s. I can run my pump at 100% with twin 1" drains and valves fully opened and they keep up without a problem. The drains have about 3" of water on top of them in with the vavles open. Now I don't run it like that normally because that creates a ton of noise from the large drop from the weir to the drains but with tuned in I run vavles at 3/4 and the pump at 75% so by duros work properly and i have a 1" drop from the weir.