You should never under any circumstance try to flush mercury down your toilet at home since it'll just contaminate the water supply, but in a closed course experiment where the toilet has been safely disconnected from a water supply and you want to flush the toilet with mercury inside of it for the sake of science, we say go for it!
Have you ever wondered how mercury, a type of liquid metal, would flush down a toilet full of water? It seems popular YouTuber Cody'sLab wanted to know too, so that's exactly what he did.
First trying with water and a small amount of mercury, the goal was to see if water could generate the forces strong enough to push the dense liquid metal down the drain. Gradually, more and more mercury is added until it comes down to trying to flush the toilet with no water at all, and just mercury alone.
As you can see, mercury is really weird. Despite being a liquid, it's denser than lead and very heavy when used in the amounts you see, so there are some expected side effects to the toilet afterwards.