[W]e were using elemental sodium for some reaction or another...Alledgedly the reaction was done, but another student (I swear, it wasn't me!!), decided to quench it by putting the reaction vessel under the faucet. All of you chemists don't need to have pointed out what happened next: A geyser of flame emitted from the sink drain all the way to the ceiling 20 ft above the floor. What really is fixed in my mind is the TA's reaction. Nonchalantly striding up to the sink, he looked at the panicked student and said: "Doused it with water, didn't we?" and turned to find an extinguisher.
I confess that I once dumped a small bottle of isoamyl acetate down the drain (Hey, it didn't say anything on the label!) and the lab also smelled like "a shipwrecked banana boat" for days.