Daniel, what I have found that works for me is to use a piece of 5/16's tubing, as you did. What I do is place the bit into the drill motor then the tubing goes all the way to the bottom against the drill motor. You should then only have 2'' protruding and the rest covered by the tubing.
2004 - 2012 2x3 flat pan 25 to 60 taps
2012 2x3 new divided pan w/draw off 55 taps
2018 - didn't boil surgery - bought new evaporator
2019 new SML 2x4 raised flue high output evap. 65 taps
made 17 gal. syrup
2020 - only put out 53 taps - made 16.25 ga.l syrup
2021 - Didn't work out
2022 - 25 taps on bags / 8 taps on 3/16's line - late start