Earthman, I did something very similar. I put some cherry Kool Aid powder in a showerhead. On Nov. 1. After a Halloween all-night outdoor horror movie festival.
So the first guy to turn it on … had blood red water pouring out on him. The shriek woke up half the hall. 
An ex-colleauge of mine owned a luxurious Lada car while at University. It inspired much joking. With the appropriate Russian accent, he and his friends called it the “Russian Land Speed Cruiser”. Eventually, it became an ongoing residence in-joke to speak in a fake Russian accent.
This theme culminated one night after a wee bit of drinking, when the Lada was driven to the Russian consulate, and several students uprooted a very dignified Russian statue from the grounds, and loaded it onto the Lada. From that day forward, their dorm was graced by that statue.
And if the Russians are listening, I do have his name and address 
I went to a coed military school for high school and my first two years at college. Pranks were on going but my favorites are these…
Stuffing feathers in a cannon before it was fired in a parade.
Dismantling an old wooden bridge and stacking each plank of wood neatly in a pile. The bridge lead to the football field and there was quite a detour to get there without the bridge.
Again with the cannon - all seniors would fall as though they had been shot during a parade in front of visiting parents when the cannon was fired.
Ha! Military humor!