external overflow vs drilled tank

The main con to external overflows is that it's very difficult if not impossible to set them up so that they are fail-proof. There are a lot of things that can cause them to fail (like power outages) and when they fail, a lot of bad things can happen like overflowing your tank and flooding your floor.

I highly recommend that you dril and build an internal overflow so you can let gravity take care of the rest... It will give you a lot of peace of mind.

-JB

 

Amen to what JB said, drilled is the only way to go!

 

Agreed, and remember, you can drill most tanks if the glass is not tempered. Having said that, I had four HOB overflows running. Now I have three and one is homemade. In the end I will have only one. My new 240 is tempered glass all the way around so I couldn't drill it. HOB's work but you have to be diligent in their care. They need to be inspected daily to make sure the aqualifter vacuum pump is flowing freely. Craig and JB are right, they are dangerous. But if you get CPR's with aqualifters the power outage worry goes away.

 

No, but it is hard to tell. The only "reliable" way to know it is is to inspect the glass very carefully. If it is tempered it should have markings. And if you can't find them, cross your fingers while you drill.

 

Nope, you need to inspect with a magnifying glass for the tempered markings like the windshield of a car.

 

in most cases that bottom is tempered but not the sides or front and back. if you have a good ear and know what to listen for, you can also tell by tapping on the glass, tempered glass will sound different. i downloaded a data sheet from allglass a while back and it had marked on there which tanks had tempered glass and which didn't, you may be able to find out for sure that way.
and you definitely want to drill if you can. i hate hob overflows.