Plumbing questions

[Martini5788]

So I am getting ready to combine my 2 tanks. Both tanks will have an eschopps 800 overflow box with a 1 inch drain and they will drain into a 20 long sump. One is 40 gallons the other is 69 gallons. I have a fluval sp4 return pump that I will use for both tanks. My question is, should I use 3/4 inch or 1/2 inch return lines? I need to order gate valves for the returns and can't decide which size to use.

 

[yellowRubi]

What size is on your return pump? 3/4?

 

[Martini5788]

Yes it's 3/4 inch I think

 

[hkgar]

Then use 3/4

 

[Martini5788]

Ok I wasn't sure if I had to cut the return lines each to almost half of that since it will completely split the flow