The pitch was, what was life like now that the pets had all gotten back to their homes and made peace with the,"flushed pets".
I thought it might be funny if, once the owners had left for the day, the flushed pets showed up to hang out their new friends, using the ductwork of the building as the means of getting around. Norman could act as doorman, giving directions, etc since he'd spent so much of the film lost in the ductwork.
Here's the very rough boards.
First the handful of beat boards to sell the initial idea:
Then...the rough pitch.