1. Using one's mouth to precisely transfer liquids using a pipette.
2. A very accurate but Darwinistic way of measuring liquids due to the possibility of swallowing chemicals.
Bob was the most precise lab tech around because of his controversial use of mouth pipetting. Unfortunately this is now on his tombstone because the retard drank acid.
Performing oral sex, especially on a scientist or laboratory worker
The attractive female lab tech asked about the dangers of mouth pipetting and if she was at risk to accidentally inhale the DNA sample she wanted to collect