Unless you recently put something toxic down the drain such as drain cleaner, he will be fine. Cats clean themselves constantly, including their paws after they have used litter boxes. Cats love to be clean, and spend the majority of their awake time cleaning themselves. They, no doubt, come into contact with some pretty nasty things regularly, but their immune systems are very well accustomed and equipped to deal with the majority of the bacteria and other nasty germs they come into contact with.Their saliva has antiseptic properties which aids them in keeping clean and healthy. Clean his paws as best you can with Dawn original dish detergent, rinse well, and he will be just fine.