When I was living in an apartment building they sent out a notice to all residents to only put toilet paper in the toilet. Apparently there are quite a few items that are said to be biodegradable, that are listed as flushable, but in reality it depends on your area and your waste disposal or treatment plants. They have lift stations and anything that cannot be disolved has to be removed and treated. Paper Towels, Napkins and anything thicker than toilet paper can mess these places up.
While a company gives us flushable toilet brushes, some older systems may not be ready for them. Contact your water and sewage or waste disposal providers to ask what you should and should not flush.