How to Size External Overflow Box...

[EuroDriver]

I'm gearing up to swap out my uniquarium for a regular 50g acrylic. I am working on a DIY external overflow box to run this type of drain system: http://beananimal.com/projects/silen...ow-system.aspx into this sump (Aqueon Proflex Model 1): http://www.aqueonproducts.com/products/proflex-sump.htm
Based on my rough calculations, the overflow chamber of the sump should be able to handle about 4.5g total, less about 3" depth at normal operation would net about 3.2g worth of overflow at shutoff.

My idea is to cut slots on the back of the aquarium at the top lip (2 slots of 7" with a 2" gap in between from the center of the tank) to create a weir and mold an overflow box onto the back of the tank, using three 1" drain tubes on 1" bulkheads.

Box will be about 16" long. I am limited to 71/2" in width from tank back to the wall, although I would like to keep it at 4"-5" in width. (Initial thoughts on dimensions are" 16"LX4"WX6"H). This should yield just over 2g overflow at pump shutoff (assuming it's completely full - although I figure it will operate at least a couple of inches lower) leaving room for residual overflow from DT and volume from the plumbing = pretty close).

Plan is to use weld-on and silicone to adhere it to the tank, or maybe just silicone.

Looking for advice/input on the following:
1) If I need a minimum volume or dimensions for the drains to operate properly (i.e, not running dry, slurping, overflowing or creating too strong an eddy);
2) Whether I should be concerned about the box coming loose and detaching due to weight/pressure;
3) Whether 1" plumbing is enough to handle silent draining; and
4) If a minimum thickness of acrylic is required.

For the record, I'm building the box but I bought a CPR CS102 overflow box in case I chicken out before I take the drill to the tank. Looking forward to this project and to your ideas and opinions. TIA

[theicecreamdan]

I'm not running yet, but I have an external overflow on my new tank 4 feet long, 8 inches deep and it sticks out about 4 inches from the back of the tank.

I'm using 1.5" plumbing for the overflows, and I'll probably use most of that depth for the overflow contraptions. For 1" pvc you'll probably have enough depth, but you might want to build what you're planning on putting in there to see if you need to go deeper.

[ajn81]

I would think for something like that you would want a minimum of 1/8" thickness on the acrylic. Though 1/4" would be safer. The deeper you go, the thicker the acrylic you will need.

I wouldn't use silicone to fasten it to the tank, you are just asking for problems. If you are experienced with acrylic, you could try and use weld-on 4 which would be the cleanest way. But if not, you could use weld-on 16 which is thicker and much easier to use and will still be cleaner looking than silicone.

[EuroDriver]

Well, got my pieces cut. Found a nice smoked gray strip in the scrap bin at the local plastics shop, long enough for all 4 pieces. Set me back a whopping $8-'n-change, including the tube of weld-on. It will officially by 18"LX4.5"WX6.25"H. Now the fun begins...