[Tx Firefighter]

Bah, no reason to get excited about the shavings. I can offer you a suggestion on that.

Take your thermostat out and bolt the water neck back down. Now, put a garden hose down the water neck and shove a rag tightly around it to make a sort of seal. Now, with the garden hose flowing at a slow trickle, do your drilling and tapping. The outflow of water through the sending unit hole in the head will flush out any drilling and tapping shavings as they occur.

A little messy, drilling and tapping a hole with water coming out of it, but it damn sure beats pulling the head. You should be able to adjust the flow slow enough to not be overwhelming, yet still steady enough to flush your shavings.