Actually Lemon Jello, Knoxx Gelatin and some yellow food coloring and an Almond Joy. Dip out 1/2 of the water from the toilet bowl, fill with boiling water, add lemon Jello and Knox gelatin, stir well add yellow food coloring to correct yellow tone of liquid, add some ice from victim's freezer stir until it starts to set. Add the Almond Joy and let set.
If done correctly it will take some work to remove but the first reaction to seeing a used toilet is to flush. This tends to put a goodly amount of "clean H2o" where is is not wanted.
Also a hundred balloons spread around and one partly filled with some obnoxious perfume. Said Victim goes around popping balloons and pops the one and it send a blessing of perfume into the air.