One of the advantages of plastic garden furniture is its ease of maintenance. Soapy water (Marseille soap or black soap) and a sponge are enough to remove dirt if it is not encrusted. If your table and chairs are very dirty, you can add a little white vinegar to your soapy water. This will revive the plastic without damaging it. Remember to rinse and dry your furniture well. A word of advice: avoid the abrasive side of the sponge so as not to scratch your furniture.