First try the liquid drain products that are compatible with your home plumbing system. Some drain cleaners can not be used with PVC pipe, so read the label carefully. Never unscrew a trap with chemicals present and never mix different types of chemicals. Many are not compatible with each other.
Traps: If you have lost a valuable item such as a contact lens or ring, removing the trap, known as a "P" OR "S" trap, will be a perfect way to retrieve the lost item.
Step 1. Place a basin or bucket to catch water from the trap. If chemicals are present use a chemical resistant bucket and wear chemical resistant gloves. Also shield eyes.
Step 2. Loosen the two end nuts of the couplings. Some can be loosened by hand, but a pipe wrench may be needed. The trap will come free and you can get the lost item, or remove the plug.
Step 3. Check the washers for any damage when putting the trap back on. Replacing the damaged washers now may save you a leak later on.