Answer:
Other terms for this handy device include doohicky, doo-dad, and whatchyamacallit.
If someone calls you this, it might be time to consider hot wax
What gets bigger the more you take away from it?
What cleans as it gets dirty only to get clean the more you use it?
What is filled with air and sometimes a gas, tied to a string and often seen on your birthday?
People take me on walks and I run and have fun. What am I?