Austinchap,
Here's a solution.
Eliminate the hole drilled in the tank.
Get a small submersible pump, put it in your sump, and put it on a timer.
Connect a hose to the pump then run the hose out the window.
Get a float switch, set it up in your sump
Connect it to the new water supply
If the power goes off, no water is supplied to the sump because the float switch has it turned off. The pump doesn't send any water out the window either.
When power is on this is what happens.
Timer turns pump on (you'll have to figure out the on off cycle, but probably like 2 minutes tops) and it pumps water out the window.
The lower water in the sump causes the float switch to activate the new water supply. It shuts off when the sump level is back up. This will repeat as long as the timer is active on the pump out the window.
It also has the added benefit of automatic top off when evaporation occurs.