New tank Plumbing questions

[ReefWelder]

I am getting ready to upgrade from my 20g long with HOB filter to a 40g breeder and this time I want to drill the tank and build a sump. I am planning on around 250-300gph flow from the return pump. Would 3/4" plumbing from the overflow allow this or should I plan on using 1"? Also I am thinking of two 1/2" return heads so I can get away without using a powerhead for a cleaner look. Tell me what you think I should change. Any input is valued!

 

[DCR]

A full siphon 3/4" should handle the 250-300 gph. A gravity 3/4" overflow will likely alternate between full siphon and gravity drain and make a lot of noise. It looks like you have two overflows. I would do a Herbie with a full siphon and an overflow. The two 1/2" returns will carry the 250-300 gph but that is not going to be a lot of circulation. I think you will still likely need some internal powerheads.

 

[Alchameth]

1/2" full siphon should handle 300-400gph so 3/4 in won't have any problem.

 

[Snoopy 67]

3/4" will be fine. No matter what pump you use DO NOT reduce the pipe size from the pump, if anything oversize it. You get better flow that way.
This is where a DC pump would do better job I see you have spots for reactors & will need more flow down the line. It's nice to be able to accomplish that with the push of a button.
Your ATO should go in the pump chamber because that is where the evaporation shows up.