English: Silicone-based caulk is applied to the underside of an upturned bathroom sink which is about to be installed. The caulk will seal the gap between the sink and the countertop, preventing moisture from getting underneath the sink. Caulks for plumbing uses typically come in white, off-white, and clear colors. Source: here entitled "Swapping out a bathroom sink" (handyman project) Note the words "public domain" note at the top of the article. Further questions, ask me (tom sulcer) on my Wikipedia talk page here.