There are several ways to remove buildup from a Pyrex dish: 1. Soak the dish in warm, soapy water for 10-15 minutes. You can add baking soda or vinegar to the water to help loosen any burnt-on food. Then, use a soft-bristled brush or non-abrasive scrubber to gently scrub away the buildup. 2. Coat the bottom of the dish with baking soda and a drizzle of dish soap. Add hot water and let the mixture soak for about 15 minutes. Then, use a plastic or nylon sponge to scrub away the stains. 3. Spray a liberal application of foaming oven cleaner on the dish, targeting the baked-on grime. Place the dish in a plastic bag and tie it shut. Allow it to soak for a few hours. Rinse off the oven cleaner and wash the dish in hot, soapy water. 4. Preheat the oven to 375 degrees F. Wash the Pyrex dish with warm soapy water and a non-abrasive sponge or cloth. Rinse and dry thoroughly. Mix 1/2 cup of ammonia with 1/2 cup of water in a bowl large enough to fit the Pyrex dish. Place the dish in the bowl and let it sit for several hours. Rinse and wash the dish in hot, soapy water.