Sump info

I agree with szrazzt, drilling your tank would be better and a good quality overflow shouldn't lose siphon.

 

...how do you make an external drilled over flow, drill it through a side wall instead of the bottom?

 

If you drill it through the back, you would need to put a box on the inside of the tank so that you get proper surface skimming into the overflow box. To do an external you cut the back of the tank down so that the water will spill out the back. Instead of flowing over an internal overflow box, it goes over the back wall of the tank and then an overflow box is attached on the back of the tank instead of inside the tank. The advantage is that you don't lose any tank space at all with it. The disadvantage is it takes up room behind the tank so that you have to move it away from the wall (unless its an in-wall unit) and you have to cut the back of the tank itself. If its acrylic then its easier than glass. With glass you can cut it with a dremel tool with the right bit. Just don't make square corners in it (acrylic or glass either one). Make it gentle curves so that you don't end up with stress points in the panel.

 

I've got a Eshopps 600gph (?) overflow. Its got a Mag 9.5 through a 3/4" SCWD, but is close to 800 gph. This type of overflow is also called a "weir" type of overflow. The "U" tube that goes from box to box is always under-water so the syphon in the U tube is never lost. When water gets below the teeth on the prefilter box the water just stops flowing. On the outside box, the water goes into the oposite side of the box from the bulk head drain, so the water level will never drop below the top of the weir. I've had this for almost 2 years now. To get the syphon started, I stick a piece of 1/4" air line into the U tube (while its in place) to the highest point in the bend and suck out all the air, then I just turn on the pump.

 

Just to clarify--a properly constructed and executed overflow will not lose siphon. If it's set up properly, the U-Tube will remain submerged on either side even when power is lost. This is the key to a properly executed overflow. Both sides of the U-Tube must remain submerged even when the power is out.

Since a picture is worth a thousand words, here's the outside box portion of a standard overflow. The inside is self explanatory, so it's not pictured. It's easily understood that the U-Tube remains submerged in the wet side (in tank) side.

In the pictures, normal operation shows the box full of water. The U-Tube is on the left, descending into the box. The bulkhead/drain hole is on the right side, bottom. The second picture shows what happens when power goes out. The box drains--and without water entering from the tank, the left side (with the U-Tube) remains static for the time being, and the right side empties into the sump.

The key to proper design is the vertical piece of acrylic in the middle that separates the two halves. Many manufacturers use two vertical pieces instead of one, so designs differ--but there is always some mechanism in place to keep standing water in the overflow box for the sole purpose of keeping the U-Tube submerged.

**The bottoms of each picture is getting cut off in this view, so click on the pic for the full proper view.

Normal Operation:



Power Outage:



For whatever reason, the bottom of the pic isn't showing up in this shot. Click on the pic for the full view.