What is the fine-grained topic of the following text: Fortunately there is a plaque on the chimney informing that the tower is infact a &apos;Stink Stack!&apos; constructed in the C19th to expel methane from the sewers carrying North London&apos;s poop and other waste to nearby treatment plants. Only return the topic.
19th century 'Stink Stack' for waste treatment in North London