I've drilled my 125 acrylic cube with water still in it. I originally had a sea swirl for my return but it vibrated and made more noise than I would like it to. Decided to drill a hole for a bulkhead on the back wall of the tank. Drained about 1/3 of the display tank water. Then I lined the surface of the water with saran wrap since it floats. I drilled the inside of the tank and all the acrylic shavings stayed on the saran wrap.