In all my frustration with the pump install I almost forgot about this. I needed to use a 1" bulkhead where I currently had a 3/4" bulkhead drilled in my sump. You obviously can't just put the hole saw against the sump and go to town or it will walk all over the place, which is why they have the 1/4" drill bit in the center of the hole saw.
I used a trick I learned as a machinist, may or may not be new to some of you. Take a small piece of 3/4" or thicker wood and drill it with your larger hole saw. Now take this board and line the hole up with the existing smaller hole on your tank/sump and tape it against the sump w/ masking tape all the way around. Now you have a guide to drill the new hole with.
If you want real precision measure from the 2 closest edges of your sump to the existing hole, now select a board big enough to line up with those edges and transfer the hole location dimensions to it then drill. Now you just have to line up the edges of the board w/ the edges of the sump and tape it in place, both holes should be on center.
Maybe it will help someone out one day. This is also a good technique for drilling holes on the edge of things where your bit wants to walk off.