Drilling Tank - Where to place holes?

Please help, I have a 125 gallon tank with a tempered bottom so I am going to drill the back. I will be putting in two 1 1/2 inch bulkheads in a herbie setup. My question is where should the holes be drilled? I was thinking about 4 inches up from the bottom of the tank and about 4 inches apart. What are peoples thoughts? I was going to put in a top to bottom overflow that was 12 inches wide and 4 inches deep. I figured this would give me plenty of room to place drain pipes for the herbie.

I want to drill the tank before the weekend.

Thanks!

Joe

 

You want to drill the holes near the top to control the back flow to the sump when the power goes out or you turn off the return pump. The lower the hole the more water that can drain back to the sump and the greater the odds of a flood.

 

if your gunna drill the back why run a herbie? just run standard overflows??

 

Yes, drill towards the top outside of the tank. The lower you do it, the more chance for a flood if things go wrong at some point. Also, the higher up and out from the center of the tank, the less structural rigidity will be taken away. That shouldn't be an issue anyway, but for exaggeration's sake, a 2" hole placed in the center and lower 3rd of the tank pane will have a good chance of breaking the glass in the future. You know, like when the tank is full

 

My thought is that by using the herbie method with a drilled back is that I could control the sound of the water flow. Also, by using standpipes I would be able to limit my exposure to having too much water flow into my sump if\when the power goes out. The primary standpipe would be about 2 inches below the surface with the backup standpipe being just above the surface of the water at normal operating height.

It is possible that I do not fully understand the herbie method or its purpose. Also, if there are any other suggestions I am open to any and all.

Tanks!

Joe

 

I really appreciate at this as I did not think that by drilling low and center could cause the glass to break in the future by reducing the structural integrity.

Tanks!

Joe

 

I would drill a hole about 4" down from the top, no more than 6-8" from a side wall.

Use an elbow and a short pipe to make a stand pipe, and use whatever method you want for noise/siphon abatement. With a proper overflow box in the tank you don't even really need a standpipe, just a strainer on the bulkhead.

The MAXIMUM flow rate is determined by the size of the hole and/or the volume of the overflow box.
The ACTUAL flow rate is determined by the return pump's flow rate.

It's a balancing act, it's not hard.

The theory behind an overflow system is that if the return pump fails the plumbing will drain, the DT water level will drain to the level of the top of the overflow box and the flow will stop.

If the internal box fails the higher up the bulkhead the less water will drain.

The tank cannot flow more water out than is returned by the pump in the sump.

...hrm did that help any? heh... I dunno... maybe i just rehashed what you know.

 

Here's an idea I just got for how to make and attach the overflow box. I would get a well made acrylic box that's leak tested, (shown in orange), drill a matching hole, and use the bulkhead fitting to hold it in place. Less risk of glass-acrylic silicone failure. Seal around all the back edges to the glass to avoid leaks between the glass and acrylic, as well as to hold the box level, but the bulkhead is what's really holding it in place.

not sure if it's overkill or not... but I think I would do this in your situation.