I drilled a 160 gallon half full about 5 years ago and to this day the tank is still running fine. It was too big of a tank to take down so that was kind of our only option. Just sprayed water on it to keep the bit cool. Hope that this helps. Ideally though, empty is good. I just drilled my tank empty but not with a dam because I got give wrong hole size dimension, so I had to crawl into the tank and drill the vertical pane. I used one hand to drill and the other to spray water. It was 1/2" glass.
Des
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