How can I find a flapper for a model T803 toilet. It is a Project Source High-Efficiency toilet

Do an on line search for your toilet model number or just ask your Lowes sales person to assist you. Have your toilet name model number if you know it and the old flapper valve. Shut the water off at the floor valve to the toilet and simply remove the old flapper valve, take it with you to your neighbor hood Lowes store and I am confident one of the floor persons will help you find the correct replacement flapper.

The Fluidmaster 3 inch Universal Flapper (model) 5403 will fit and take the place of the original equipment supplied by Project Source. The 5403 which has several settings will adjust to fit both the mounting pins and is big enough to cover the drain seat.