Shower drain sealant is a waterproof and flexible material used to seal the gap between the drain flange and the shower base, preventing water leakage and protecting against mold and mildew. It is made with various ingredients, including silicone, polyurethane, or butyl rubber, and is applied as a bead around the drain flange to create a watertight seal. Sealants from manufacturers like Aquadefense, DAP, and Loctite are available at major retailers like Amazon, Home Depot, and Lowe’s.