Rinsing is extremely important. Fill the wash basin with two or three inches of water until the bottom part of the cat's fur starts to float in the water. Keep rinsing until there is no residue. Use a cup to scoop the basin water over the cat's body and keep doing it until the coat is free of shampoo. Empty the soapy water from the sink and refill with clear water as needed.
For more information in grooming your kitty, go to Grooming Your Cat.