What size hole to drill in tank

I have a 29 gallon tank, and I'm looking to add a sump/refug. I plan on drilling the holes myself however I cannot find any info about what size to drill. I plan on using a mag 5, and its ~4ft down so that will give me around 300gph into the tank. It uses a 1/2 connection however I believe if I use a 1/2 inch outflow that might be to small. Does anyone know of any web site on pipe flow gph or how to calculate or figure out the correct hole sizes?

 

I would drill for a 1" bulkhead. Use a smaller pump to return, or use a ball valve to control the flow back into the tank. the bulkhead should tell you what size hole is needed. My 1" needed 1 3/4" holes

 

I drill tanks for my LFS' and I would tell you from experience to go with a 1" hole. They put 1" holes on tanks from 20 - 90 gallon. 3/4 is too restrictive even with a thin walled pipe. If you go to the website make sure you get a 1" hole bit not a 1" bit because like Zach said, the bit is bigger to accomidate the threads and actual bulk head. You can't go wrong with a 1".

 

I agree. I went with a 3/4" drain on my 20G and I'm wishing I went 1" instead. It works, but I'm maxed out on my return rate.

 

Perfect, this is just what I needed to hear. Thanks alot

 

Like ZachB said my 1" bulkhead needed a 1 3/4" hole

 

Yup, get a 1-3/4" diamond hole saw bit. When you drill, go SLOW and cool the glass and the bit frequently. I used a spray bottle and kept the bit wet. I completely stopped every 3-5 mins to let the glass cool, and ran the bit under running water to cool it off and to get rid of the powder. The glass will become a ultra fine sand powder. I also put gaffers tape on the inside of the talk where the hole is drilled to keep the hole from falling out. But just remember to go slow and don't add pressure to the drill, just let the bit do the work.

 

Just a heads up... I know you may not be ambadextrious and I probably hacked the spelling but... I use plumbers putty and make a little reservoir for what ever cooling liquid you decide to use. Everyone has their theories from cooking oil to water. All I can say is don't push. I found it way better to use a 12v Ryobi because they are light and not full of torque. Put a towel where the "coolant" will fall so you don't make a mess and to catch any small fragments of glass that chip. Yes, 1 3/4" bit is used for a 1" hole.
I get my bits here and they are good.

Glass-Holes.com dope aquarium stuff : Glass Hole Cutters

 

The water gets HOT too. If you use a reservoir like Optimist suggested, make sure you replace the water when it gets hot.

 

for cooling my glass shop says antifreez is what to use?