I was inspired to do this costume for my daughter because she was in the process of potty training at the time. Luckily her size was roughly proportional to an actual toilet. She really enjoyed wearing it too because the toilet lid opens to reveal a bowl that functions as the candy receptacle; making it a fun and interactive costume.
You will need:
1. a cheap plastic bowl with a lip about 12"
2. enough sturdy wire to circumvent the bowl (I used a wire hanger)
3. a piece of cardboard large enough to cover top of bowl
4. hot glue
5. a roll of poly-fil foam (24" x 48")
6. and silky white fabric (24"x 48")