No one really answered that question, till you. So it's possible to attach the overflow then just use ball valves till I add a sump later on? I wasn't planning on adding livestock till after drilling. Just wanted to get the cycle going and from what i've seen drilling vertically while the tank has water in it isn't bad as long as you take the necessary precautions to prevent glass dust from getting into the tank
If drilling vertically [i've done it] cover the back of the hole with duck tape and spray the area with water. The bigger issue is keeping things cool while drilling. I soaked a papertowel with cold, refrigerated water and stuffed it into the center of my hole saw drill bit. This allowed the cold water to be 'whipped' out while drilling. I'd also put a towel underneath where you're drilling. You shouldn't have any issues with not having the sump set up while cycling the rock int he tank. Like you said, just use a ball valve [or don't fill the tank up all the way]. Make sure that you have flow in the tank though while cycling [throw a powerhead or two on the glass]


