On my yet-to-be setup 180, I prematurely drilled a coupla 1-3/4" holes in the high back wall ( for 1" bulkheads) for an overflow setup that I later decided would be too restrictive, flow-wise.
After seeing this thread, I decided two 1-3/4 holes would be fine, though, which was great since that's what I had already drilled!
I have created two weirs about 5" tall, 1" front-to-back, and 24" long out of 3/8" thick glass. These will be siliconed in soon (yeah right. This whole project has taken about a year too long. More time for ponderin'!)
On the outside of the tank I have two boxes similiar to what ya'll have here, each with two 1" bulheads on bottom, for a total of 4 x 1" bulkheads. Beats just two!!
So each long skinny weir feeds a 1-3/4" hole in the tank, which in turn drains into a box on back with two 1" bulkheads. although I have created the weirs and boxes, I have yet to attach them to the tank.
Point of post (finally):
I too had fear of torquing out the bottom of my boxes with bumps to the plumbing, etc, despite my thicker-than-usual glass. So I cut a similiar sized piece of 3/8" acrylic, cut a 1-3/4" hole for the bulkhead, and siliconed it to the bottom of each box. Nice thick layer of silicone, too. I also tightened the bulkead in place during curing, so that the planes of the acrylic and glass would remain parallel.
I guess this would work just as well (better?) with an extra pane of thick glass sandwiched to the botom of the box.
