To begin with, (speaking from experience) this is a great project to do BEFORE you have cleaned your bathroom and NOT after. 'Kay?
This little activity is nothing new, but it was something that I discovered had unintended but beneficial side effects. My kids LOVE to play with baking soda and vinegar. They love watching it bubble up and fizz and I love that their "experimenting" is completely safe. I used to give them the baking soda to play with on a cookie sheet but quickly discovered that it didn't stay there, so in a stroke of genius I decided one day to pull the drain on the sink in the bathroom, fill it with baking soda, and let them play in there. When I was finished I would just wash it all down the drain and be done, no huge messy clean up needed!
What I discovered was that after this play time not only were my sinks clean, but also they drained a lot better! I knew that baking soda and vinegar were good for cleaning and I knew that you could use them to clear a drain, but I didn't know that kids' fun could result in something being cleaner at the end than it was in the beginning. Score one for Mommy!
So now whenever I have a slow drain I dump some baking soda, pour some vinegar, and let the kids have at it. But they don't know that they are cleaning so shhhh....