Pipe repairs can be costly, do stay away from flushing these things to avoid damage.
Family Handyman said, “Most people know it’s a bad idea to pour grease down your kitchen sink. It’s equally important not to do it in the toilet. Warm grease runs down your drain until it cools in the pipe, where it congeals to start forming a clog.”
Also stay away from flushing bleach, tissues, paper towel, cat litter, and hair!
Finally, don’t flush your fish either. It will either die in a few minutes or cause ecological harm!