K.S.
We are going through the same thing, but the big potty is Ok at home just not anywhere else!
I have one of these portable, fold up potties that is great. The liners aren't the cheapest, but it is so nice b/c you can use it anywhere instead of the big potty and just throw the liner away. It folds up so small it fits in my purse. http://www.toysrus.com/search/index.jsp?kwCatId=&kw=p...
Good luck!