Where to drill holes for the overflow?

[Dule T&T]

Hello everyone.

7 years ago my old tank exploded and in the emergency I needed to get a new tank right away in order to save all my animals.
Because where I live finding already made large enough reef tanks to buy is pretty much impossible, I was forced to buy a regular tank without the overflow. Because animals couldn't wait anymore I put them inside of that tank and after that I needed to be creative and find a way to make it work.
I solved the problem by installing sump on the side of the tank (on the right side in the picture) and made sump drain into the tank instead of usual tank draining into the sump.
It worked just fine for the last almost 7 years.

....But, right now I need to move the tank to another location because of house reconstruction (you can notice messy construction work on the wall behind the tank)... and because new location doesn't allow the same setup, I need to drill the back glass for the overflow and make a regular sump bellow the tank.

I was thinking to drill 3 holes 2 inches in diameter, and because tank is pretty much narrow but long, in order to save as much space as possible I will make the overflow box behind the back glass.

Can you please advise if this location (top middle, as shown in the picture bellow) on the back glass is safe and won't affect tank's structural integrity.
(I am worried because middle area seems as the one that is under most of the pressure and where glass always bends slightly)
Also how far from the top of the tank should holes be drilled and how much space should be between the holes?

It's a glass tank (18 mm thick glass), 10 feet long, 2 feet wide and 31.5 inches high.
350 gallons.

Thanks.

Picture of my tank:

 

[Dule T&T]

Anyone ???

 

[mfinn]

The middle seems to be a common place to drill for overflows.
The diameter of the holes should be exact the diameter of the bulkhead fittings you plan to use.
The distance from the top will be determined by the inside and outside plumbing you plan to use.
Just a wide guess I would give at least an inch between the bulkhead fittings outside nuts.

I know there are pre made overflow kits that will come with patterns and even drill bits.
Synergy, eshopps, etc.

On my 240 I have an external overflow box ( with an internal box), but the tank maker had the back glass cut with a dip in the top edge for a flow through design.

 

[DCR]

Need more design detail about the overflow. Are you buying an overflow kit or are you going to make it yourself? If the elevation of the holes does not affect the level in the overflow, then I would leave at least 3-4" of glass between the edge of the glass pane and the edge of the holes. There is not a lot of stress at the top of the tank. As long as the holes are reasonably spaced apart it should not affect the structural integrity of the tank.

 

[dadnjesse]

You should get the overflow kit first then there should be insructions were to drill them. The Synergy Reef is popular.

16″ Shadow Overflow V3

New Shadow V3 Overflow Kit – Just arrived!

synergyreef.com

 

[edd59]

buy an overflow kit like mentioned, it comes with a template so you drill holes in the correct location. those holes will determine your water line/level. make sure your tank is drillable, type of glass.

 

[Dule T&T]

Thank you all

 

[Dule T&T]

Need more design detail about the overflow. Are you buying an overflow kit or are you going to make it yourself? If the elevation of the holes does not affect the level in the overflow, then I would leave at least 3-4" of glass between the edge of the glass pane and the edge of the holes. There is not a lot of stress at the top of the tank. As long as the holes are reasonably spaced apart it should not affect the structural integrity of the tank.

I was thinking to make my own overflow, but now I am actually considering buying one.

No, position of holes should not affect the water level.
Also, if the edge of the holes are, let's say 4" from the top edge of the glass, how much space would you leave between the holes to be "reasonably spaced"?
Also does it matter if I drill 2 or 3 holes? I am guessing the less drilling the better? I would prefer 3 holes though for a better GPH rate.

 

[mfinn]

Also does it matter if I drill 2 or 3 holes? I am guessing the less drilling the better? I would prefer 3 holes though for a better GPH rate.

This may help

Overflow Boxes and Drain Styles - Durso, Herbie, and Bean Animal

Decide which of the three most common types of drains and overflow boxes is right for you and your tank.

www.bulkreefsupply.com

 

[edd59]

I was thinking to make my own overflow, but now I am actually considering buying one.

No, position of holes should not affect the water level.
Also, if the edge of the holes are, let's say 4" from the top edge of the glass, how much space would you leave between the holes to be "reasonably spaced"?
Also does it matter if I drill 2 or 3 holes? I am guessing the less drilling the better? I would prefer 3 holes though for a better GPH rate.

on an over the counter overflow the weir attaches to the bulkheads, so yes that will effect the water level.