Advise on return pump and plumbing sizes

[AlexF]

I have a 55 gallon DT and I am adding a 30 gallon sump. My HOB overflow has two 1in drains what size pump should I use and how big of a return line do I need.

 

[reefwatcher]

Mag 3

 

[jdl513]

I would go with the Sicce Syncra 2.0.

According to their flow charts if your sump is 4 feet below the top of the tank the 2.0 should run at roughly 400 gph.
If you want more flow the 3.0 should bump that up to around 600 gph.
Two one-inch drains should have no problem handling either pump and both come with 3/4" outlets for the return line.