If you need to use the bathroom then there are plenty of good places for you to do that in the city, which you are experiencing from your seat in my bus/boat.
Wow! Amazing! I just love the city. You're sitting in my bus that's also a boat experiencing the city of Boston with your eyes while I tell you facts about the city in a funny and/or quirky way.
I'm a Boston Duck Tours tour guide. We're driving on the roads with a car that's also a boat. We're on the roads now driving through the city. Hold on!! We got a red light. We have to wait until it's green. We're stopping now in front of the crosswalk at a city intersection. On your right is a building. On your left, another building. Soon we are going to go in the river and drive the car/boat to a different part.