Overflow plumbing question

[flmlly]

I recently purchased a used 90g aquarium that I am trying to clean up and get started. It has in internal overflow with 3 holes drilled in it: two holes are drilled for 3/4" pipe & one (in the middle) is drilled for 1" pipe. It was set up with a herbie overflow before- the two drains were the 3/4", and the return was the 1" that split into two loc-lines and returned to the tank. He said he'd had it setup that way for as long as he'd owned it without issue.

My question is, is it acceptable to leave it this way? From what I've been reading on here it is ideal to have the drain be the largest pipe ID. My thought was to change the middle 1" to the main drain, and one of the side 3/4" lines to the emergency drain leaving the 2nd 3/4" hole as the return that I'd split back into the tank. My only other thought would be to possibly enlarge all 3 holes to 1"(?)

I appreciate any feedback I can get.

Thank you.

 

[Biglew11]

Ideally you'd want the Emergency drain to be the same size as the main drain. You might set up one 3/4 as a return line one 3/4 as the main, and the 1inch as the Emergency.

If the bottom isn't tempered you could make the other 2 holes larger.

if the glass is tempered is was drilled before it was tempered, And you will not be able to drill it.

 

[Coralsdaily]

Agree with Biglew, use the 3/4 as return. And you can chose to use either as your main drain, but personally I'd do 1" as my main drain and 3/4 as auxiliary.

 

[KStatefan]

I would plumb it as @Biglew11 said. If the main drain is able to flow more then the emergency you only have a partial emergency.