Put a plastic bottle in the toilet tank

Take a small soap bar, put it in a thin sock. Tie the mouth of the sock.

After that, place the soap sock into the toilet tank. Note, do not let the soap sink to the bottom. Rest one end of the sock on the edge of the tank and use the lid to cover it to keep the sock suspended in the water. The soap will slowly dissolve into the water. When you press the toilet flush button, the soapy water will flow out and help remove dirt and odors.