Stop a Moen faucet from dripping by replacing the cartridge. Moen cartridges are readily available, but the company makes several different styles of cartridges, so remove the old one and take it to the plumbing supply store to ensure you get the right part.
Begin the process by turning off the water supply to the faucet. Use the valves under the sink to turn off both the hot and cold water. Once it is off, turn on the faucet to bleed any residual pressure.
Remove the handle from a single handle faucet by gently prying the cap from it and using an Allen wrench to turn the set screw counterclockwise to remove it. Lift the handle from the faucet. Use a Phillips screwdriver to remove the screw from the handle adapter and lift the plastic pivot stop ring off the fixture. Use slip-joint pliers to turn the retaining nut counterclockwise and use the tip of a flat-head screwdriver to remove the retaining clip.
Use the pliers to grip the top of the cartridge and twist it back and forth to loosen it. If you have already bought the replacement kit, place the plastic spanner tool over the cartridge before attempting to loosen it. Once it is loose, lift the cartridge from the faucet. Replace it with a new cartridge and reverse the steps to complete the job.