hmmm, the tank would not be empty while doing this, just the overflow boxes. I emptied them to convert from a herbie to a durso and the inhabitants didn't seem to mind with just the flow from the Vortech's.
Unfortunately it will not be possible to drill the glass, the tank is built in to a wall (two sided), so the tank is exactly as wide as it can be, there's no leeway or access on either end.
Here's the pics from when the plumbing was being built, they're not complete, but you get the idea:
South end - before the union and gate valve was installed
North end - before the union and gate valve was installed
Whole cabinet, before the union and gate valve was installed
the union and gate valve. It's designed so that when that lever is to the right, water flows in to the skimmer chamber and does a big U through the whole sump, when the lever is turned to the left, water exits directly in to the bubble trap right before the return chamber, bypassing 3 of 4 of the sump chambers. This wreaked HAVOC with the herbies, having them plumbed together like that just isn't possible if you want a stable system. If I had the trickle drain be on the right, and the full siphon drain on the left, the water in the trickle drain wouldn't need to make a 90 degree turn, but the full siphon would (though I doubt that would affect anything)
