“Yeah, someone might slip dragon dung in it again, eh, Perce?” -- Fred Weasley (GF5)
Dragon dung is a useful material taken from a dragon. Dragon dung is sold by the barrel in Knockturn Alley (CS4). This may be related to its use as compost in Herbology. Great for sending to Percy Weasley at the Ministry of Magic as, uh, an example of fertilizer. Yeah, that’s it (GF5).
Dragon dung compost is a collectable item on Pottermore. It is described as: "this superb fertiliser is used by expert Herbologists. Bathing may be necessary to get rid of its pungent aroma."
Other useful materials from dragons are used in Potions such as dragon's blood.