The dirty blast, despite having a drink option, cannot be drunk nor emptied. It is useless after the quest. The fastest way to make it is going to the Grand Exchange and buying a fruit blast then add the ashes.
This drink was part of a spell trapping the Culinaromancer in another dimension. A century later, the descendent of the spell creator mistook the spell for a grand banquet and requested aid in obtaining the ingredients, including the dirty blast. He recreated the spell, accidentally freeing the Culinaromancer from his prison.