I am not sure when mop buckets started having drains in the back, but it made for a great prank that people just keep falling for. The problem with it though is two-fold: 1. you have to tilt the bucket (preferably empty) forward to reach under the hard flap that the handle/ faucet is hidden under to even reach it without any strain to open or close it. 2. Some nights its never worth the energy even when the bucket has to be filled with water and floor soap because you never know if someone else thought of the same prank you did or if you are the one falling victim to your own prank cause everyone else is too afraid to use the bucket thinking it leaks.
Still the payoff is often worth the effort like my effort on a nightly basis. I am not a janitor but at the end of my work night I am required to mop as is the requirement of several others I work with at the heated hell of a factory. In fact it's often time hilarious to have that drain open and let someone else grab the empty mop bucket and go to the hallway water hose to fill the bucket watching him wait to fill it with water and suddenly noticing his feet getting wet and a large pool of water going all over the floor that other people have to walk through in order to punch out at the time clock. Unfortunately this has resulted in work related injuries to some innocent people, which is why I won't disclose the name of the company nor the town or state in which this has happened (believe it or not this would narrow that down quite a bit more than you would imagine considering my co-workers referred me to this site...as it is just listing this prank already kinda narrows it down enough as it is)