That does sound a bit beefy.... I use a 4'X1/4" bell hanger bit, and just use a level before starting the second hole in the roof - then the hole saws.
I did however hear of a simular set up - but for underground. Thread the bit on the conduit, and the other to the fitting that pumps water in and a large drill. When finished remove the bit, and drain the water out of the conduit and use it.
