Help drilling a tank

[so_so_reef]

I recently bought a cheap aquarium that only has two holes in the base, and came with a durso down pipe.

I want to convert the tank to a herbie style system so I can run it silently with a gate valve on the main drain.

I’m trying to work out if I can safely drill a third hole in the base. There’s plenty of space in the weir box for a third pipe.

The existing holes are 40 mm (1.57 inches), 20 mm (0.78 inches) and the new hole I’d like to drill is 25 mm (0.98 inches). The glass is 8 mm (0.3 inches) and the aquarium is an 90 l (24 us gallon) cube. Apologies for the metric values!

I might be wrong, but I gather best practice is to leave a distance the diameter of the hole away from the glass edge. I’m not sure how much space I can have between holes though.

I’ve checked and there’s enough room for the bulk heads to fit easily. The picture below shows the existing holes and the 25 mm drill bit.

Any thoughts would be greatly appreciated!

 

[twentyleagues]

Herbie only uses 2 holes. Bean animal uses 3. Have you done anything to check if it is tempered? Will 3 bulkheads fit in the space?

 

[so_so_reef]

Yes all the bulkheads fit with plenty of room. It’ll be a herbie but the third line is a return.

 

[SaltyWalty]

I’ve drilled several tanks and this seems like it would be fine.
Are you gonna run the 40mm hole as the main drain, The new 25mm hole would be secondary drain, and the existing 20mm hole would be return line?

 

[so_so_reef]

I’ve drilled several tanks and this seems like it would be fine.
Are you gonna run the 40mm hole as the main drain, The new 25mm hole would be secondary drain, and the existing 20mm hole would be return line?

That was the plan! The max theoretical flow on the tank given my return pump is well within the capacity for the 25 mm secondary drain.

 

[so_so_reef]

I’m mainly worried about how close the holes can be. I can’t quite get it so there’s a 40 mm hole between the largest hole and the new 25 mm one, whilst maintaining at least 3 cm away from the edges.

 

[SaltyWalty]

That was the plan! The max theoretical flow on the tank given my return pump is well within the capacity for the 25 mm secondary drain.

Yeah sounds like a solid set up! I definitely recommend having a template to help hold the bit still while you start drilling. Makes it a lot easier and more accurate. I’ll usually use the bit and drill through a scrap piece of acrylic or the same sized bit through a piece of wood, then use either of them as a template.
And constant water running onto the bit while you are drilling

 

[so_so_reef]

I did a double check on the glass today with some polarised glasses and doesn’t look tempered to me.

 

[SaltyWalty]

Looks good to me. Also given it’s already got two holes in it’s, good chance it’s not tempered.
Have you considered doing a full build thread? I’d be interested in following along as the tank of finished!