Rarity is a mare of high standards on just about everything. That includes hygiene.
So naturally when her toilet clogs up she's going to panic. But once that's over with what is she going to do?
With the local repair company busy with other customers Rarity decides to call in a new friend of Fluttershy's to get the job done.
(A quick little idea that came to me after a thread on the Crossover group. Warning: Sanity not included. Takes place after Rayman Raving Rabbids 2.)