Two drain hole in overflow?

[Exodon]

Hi, everyone.

I've been lurking the forum for awhile now and finally decided to make my first post main reason is because often time my questions have already been asked and answered (hooray the search engine). Though, I recently ran into a situation and could not find an existing thread similar.

Recently, I bought a used 75 gallon tank with corner overflow that comes with 3 drilled holes. Was wondering if I could use 2 holes to drain and 1 return? Or should I just plug one of the hole off? And what is the main purpose of having 3 drilled holes in an overflow instead of 2? Thanks in advance for your help!

Oh yeah, Im currently running freshwater with a 55gallon wet/dry sump.

 

[ragin_cajun]

That's so you can set up a Herbie Overflow. A drain's REAL important, so it's nice to have a backup drain in case your main drain gets clogged up.
http://gmacreef.com/herbie-overflow-reef-tank-plumbing-method-basics/

 

[Exodon]

Thanks for the fast reply, ragin. Will definitely look into that.

 

[duanes]

Agree about the protective redundancy, if you make each overflow tube slightly taller than the next, the chance of all 3 tubes becoming plugged at the same time, and an overflowing tank is reduced. And overflow tubes (especially 1, maybe 2), can easily get plugged with debris, plants, snails, a dead fish and cause an overflow, 3 is the insurance that gives you the time notice, and clean them out, before a problem gets out of control.