Smooth the inside, outside and edges of the pots with sandpaper. Make sure loose particles and any sharp spots are removed. Sand the outside but not the inside of the dish because a rough finish will give birds better footing.
Coat the inside of each pot three times with sealant to protect against moisture damage. Let it dry before coating exterior areas. Paint the inside of the dish and let it dry before coating the bottom.
Turn the pots upside down and stack them on top of each other with the largest on the bottom. Use a pencil to mark where each pot meets the next to show which parts of the pots will be exposed. Apply three coats of sealant to the exposed areas of the pots for protection and to achieve a glossy finish. Let them dry before assembly.
Assemble the birdbath atop the paver to avoid contact with moist soil. Place the paver in a part of the landscape that you can view inside from a window. Choose a spot close to shrubbery or low tree branches so birds will be able to make a quick getaway if a cat shows up.
Turn the largest pot upside down and place it on the paver. Place the medium-sized pot upside down over the base of the biggest pot. Check for stability. Apply a bit of weatherstripping inside the lip of the medium pot if there isn't a snug fit. Flip over the smallest pot and place it over the medium pot. Repeat the weatherstripping procedure if necessary.
Center the dish on top of the column of pots. Don't permanently connect it to the birdbath, because it is necessary to empty the dish and scrub it at least twice a week. Add water to the dish and get ready for birdwatching.
Mount a misting device on the bushes or tree next to the fountain so water droplets will ripple the birdbath's surface. This optional touch will more easily attract winged visitors.