Overflow drain size for a 180?

[RobB'z Reef]

Getting a 180 (roughly 6x2x2) and am going with a modular marine overflow. I'm planning on two return pumps just trying to get a handle on drain sizes and return line sizes. MM says they are plumbed in the box for 1 1/2" drains. Is this overkill or am i fine with a gate valve? Should my return lines be 1" or is 3/4" adequate? I was thinking 1" with two 3/4" locklines split on each return on the inside (i found 1" lock lines on some site...). Any feedback is much appreciated, this is my first tank since 2005 and I'm up-sizing quite a bit!

 

[lapin]

1 1/2 drains. 1" returns and its fine to spit them. I did this on my 125 with great sucess