Caulking around the base of your toilet will give you a clean bead of sealant there, preventing dust and moisture from gathering in the line where the base meets the floor. Whether you've just installed a new toilet, or are caulking around one that's been there awhile, use the opportunity to level the toilet bowl before you caulk, which will make it flush more efficiently. Silicone caulk is best for toilet bases, as it seals better than latex caulk and stays flexible.
Loosen the two floor bolts on either side of the toilet base, using a socket wrench.
Set a level over the rim of the toilet. Slide plastic shims under the toilet base, adjusting as needed to level. Tighten down the bolts once the toilet is level. Cut off excess parts of the shims sticking out from under the base.
Set the tube of silicone caulk into the caulking gun. Cut off the plastic tip of the tube, using your razor knife. Make the cut about one-quarter inch wide at a 45-degree angle.
Stick a nail down into the hole to break the seal. Compress the caulking gun trigger until some caulk is expelled from the end. Press the pressure-release bar at the back end of the gun to stop the caulk.
Hold the tip of the tube at the rear of the toilet base, angled downward to the floor. Compress the trigger, then pull the gun slowly back around the base to lay a smooth, even line of caulk. Watch carefully as you caulk to ensure you are completely filling the line between the bottom of the toilet base and the floor, with no gaps.
Caulk all the way around the toilet base. Wet your thumb and immediately run it around the base, flattening out the caulk into a smooth line. Clean your hands with paper towels.