Question:
A common question about repairing drain pans on the vehicle
is how do you keep chips from entering the drain pan?

Answer:
Using some general purpose grease on the drill and tap will help
prevent chips from going into the drain pan. Using a low RPM or
drilling by hand would further reduce the chips into the pan. 
Because we are only removing the old threads with the drill, there 
will only be a minimal amount of material removed.

Optional tip to keep chips out of the pan would be pouring the old oil 
back through pan to flush any remaining chips as it drains. 
Also remember the filter is there to catch any debris from normal engine wear.