Many say "DRILL-ling." I say "DRY-ling." Drei is German for three. The word "dreiling" (drilling?) refers to a 3-barreled gun in German, among other things. A 2-barreled gun is a "zweiling" (ZVI-ling), with the word "zwei" being German for "two", and a 4-barreled gun is a "vierling" (FEAR-ling), with the word "vier" being German for "four."
How do you say it?