It isn't easy to write a poem about a subject that lends itself to scatalogical humour rather than lyrical beauty. You might take inspiration from a story in Rohinton Mistry's short story collection Swimming Lessons. The character is an Indian immigrating to Canada. His experience is hilarious and sad because he cannot ease his bowels in a western style toilet. From what I recall he gives up and is heading home when he finally succeeds on the flight back.
You could also refer to Jonathan Swift's poem The Lady's Dressing Room to see how he deals with such an un-poetic topic. The subject is similar to yours but with different emphasis and, if I may add, an entire different outcome for "Celia!Celia! Celia shits".
Satire is your best friend in this attempt if you want to write a poem that people will read with some attention and not just consider vulgar.