The Home Depot and DoItYourself offer good tutorials on how to clean, repair and replace bathroom sink P-traps. This plumbing job takes approximately two hours and is easily accomplished.
Common reasons to remove a P-trap are that it is leaking, clogged or broken. To remove a P-trap, place a bucket beneath the drain to catch water and debris. Turn off the water supply valve, and unscrew the nuts using a pair of pliers. Wearing rubber gloves and a face mask is recommended to protect your hands and avoid breathing mold spores.
To clean the P-trap, empty its contents into the bucket, and clean with soap and water. Use a bottle brush to remove any remaining residue.
If a new P-trap is needed, insure proper sizing by bringing the old P-trap to the store as a reference.