500g overflow box plumbing question?

[Autonet]

starting on my 500g internal overflow box plumbing and there are 3 holes in each overflow( 2 x 1" and 1 x 3/4"). Normally there are 2 holes in each overflow box, one for input 1" and output/return 3/4" so why the extra 1" hole for or should I just close it up. Any suggestions??

[mgarrido]

With all 4 1" drains you should be able to drain into your sump 2400gph which is good imo for a tank that size, I'm assuming that you are going with a big sump and at least 1800gpg return pump

[SunnyHouTX]

Probably for a herbie overflow setup, which would make for a very silent overflow.

[Autonet]

100g wetdry. I was thinking of 2 x 1" and 2 x 3/4" drains and 1" return w/ 1800gph return pump.