Things You'll Need
Bathroom cleaner or bleach
A bathtub drain is typically composed of a metal fixture situated in a hole at the bottom of the tub. The drain is constantly exposed to water, soap, germs and moisture than may cause mold or rust over time if the drain is not sealed properly. Applying silicone caulk is the most effective method of sealing a bathtub drain. This waterproof, multipurpose adhesive compound is a common sealant for household applications and will help preserve the condition of your drain.
Remove any old sealant from the drain by treating it with a commercial caulk remover according to the manufacturer's instructions. Cut through the existing caulk with a utility knife once it has softened and peel it from the seam using needle-nose pliers.
Clean all existing mold or grime from around the drain before proceeding with new sealant. Simply apply a bathroom cleaner or bleach to the affected area, and wipe it with a rag.
Cut the tip on a tube of silicone caulk using a sharp pair of scissors. Insert a stiff wire into the nozzle to puncture the seal, and load the tube into the caulking gun with the tip facing away from the trigger.
Apply a bead of the sealant 1/4-inch thick or less into the seam of between the drain and the bathtub. Keep steady pressure on the trigger while you drag the tip of the gun around the circumference of the drain.
Moisten your finger and glide it quickly over the freshly applied caulk. You can also use a craft stick or the back of a plastic spoon to smooth the sealant. Allow it to cure for a full 24-hour period before using the tub.