Mix trisodium phosphate with warm water in your bucket. Add 2 tbsp. to every gallon of warm water. Trisodium phosphate is a harsh chemical so you will need to be careful to not get it in your eyes or mouth. Wear gloves and goggles while mixing and applying it.
Cover the area beneath the floor you will be repainting with a drop cloth or newspaper. Wipe the entire wall using your sponge and trisodium phosphate solution. This will clean the walls and assist in removing pet odors before you begin painting the wall.
Fill your paint tray with an oil-based primer. Water-based primers will not mask pet odors. Once your wall has dried, tape off the borders of the wall with your masking tape.
Apply the primer to your walls in an even coat. Paint the primer on your wall using a zigzag motion with your roller. Do not leave any areas unpainted. Allow primer to dry.
Paint a layer of oil-based paint over your primer using the zigzag painting method. Apply another coat of paint once the first coat has dried. After your wall has dried, carefully remove the masking tape and the drop cloth.