You can purchase a new seal if the toilet is a Domitedic toilet. For a temporary fix that worked with me. get some rubber gloves, shut off the water, open the valve with the peddle and clean the seal with vinegar or a non abrasive cleaner like Dawn. Then put the water on so the cleaner is rinsed off. Turn the water back off and empty the bowl. Spray some silicone on the seal and in the trap. Let it sit for a moment. Then turn the water back on. It should hold water as long as there are no tears in the seal. BE SURE NOT TO DROP THE CLEANING CLOTH IN YOUR TANK.