It is needed along with a Rotten tomato, an Eye of newt, and a Greenman's Ale for the Recipe for Disaster quest. The Dirty Blast, despite having a drink option, cannot be drunk nor emptied. It is useless after the quest. The reason this disgusting drink is to be supplied by the player is not to make a wonderful dish. The Culinaromancer's recipe is in fact a powerful food-magic (as explained by the gypsy when you ask her what happened) and by preparing this recipe, the Lumbridge cook inadvertently revives the Culinaromancer.