Why do you think swift describes Gulliver urinating and defecating?

You're referring to the incident in which Gulliver, a giant to the Lilliputians, puts out a fire in the Queen's apartment by relieving himself on it. Of course, no Queen is interesting in residing in a urine-drenched flat, so Gulliver's good intentions garner him no good will.

Some of Swift's allegories are debated, but probably he's illustrating the message that common men with their common sensibilities can never be sure of winning royal approval.