can I drill three bulkheads into one overflow?

I want to drill three holes in the bottom of a 29, as close together as the bulkhead flanges will let them be, which is about 3/4".

Are there any rules governing how close I can put these bulkheads to each other? I have done two very close to each other, but not three.

 

I have not seen anything in writing (I'm sure that it is out "there" somewhere). I used all heavy duty blkds. So, by the time I allowed for enough room to rotate the nut/blkd with a wrench....there was plenty of glass...I followed the thought that between the center line of one whole to the edge of the glass or edge of another hole should be no less than the diameter of the whole which was drilled.

So, when I drilled my tank, I focused on "just enough" space to install the blkd and fittings. As it turned out, I found this to be the most limiting factor. In one case, there is just enough room to fit the blkd through the hole, then install the fittings by rotating the blkd. Once the fittings were installed then I tightened up the blkd to set it in place.

Have fun with your build...

 

I came across a thread about a week ago, someone had posted recommendations for spacing (in glass). I believe when i found it i did a search for "Drilling".
I'll see if i cant find it

Found it
http://www.3reef.com/forums/reef-aquarium-articles-how-tos/drilling-glass-aquarium-54340.html

Scroll down, there is a formula..Hope it helps

 

Are you sure the bottom is not tempered?

If you are not positive, don't drill. Also, why would you need 3 holes for overflow drains in a 29g?

2 should be more than necessary.

 

Yes, I'm sure it's not tempered - good point though.

The overflow will contain the return, the drain and the emergency drain (herbie setup), hence the three holes. It's going to be an improved version of this tank, with no plumbing visible from outside the tank on any side:

 

That will look very nice sitting there.

 

Ahh, peninsula style. I see why now.

I would still only drill 2 holes near each other, about how AGA aqueon does.

The third one, the return, I would make part of the island of rock a bit away from the 2 other holes to keep some structural rigidity to the tank. At bare minimum, I would make it a good 6-8 inches away from the other 2 holes.