Where do food truck people use the restroom?

I hear great things about food trucks. People love them, and there is always a line whenever I see one parked. But one thing has always kept me away from ordering food from a truck: Where do they use the restroom? In my local town, food trucks regularly park along a busy highway. They might be there for 6-8 hours if they come for lunch and dinner. From my perspective, they have nowhere to use the restroom. This question is why I have never purchased a meal from any food trucks.