Potties are used to quick save your game.
First one is in Chapter 1. You will find a cell with a sleeping prisoner inside. Outside the cell is a box.
Break it and you will find your first potty.
Second one is also in Chapter 1. You will find a cell with a prisoner that want's for you to free him.
After obtaining the key, use it to unlock the cell with a medal to the right of the cell with a prisoner.
Do not use it on his cell before doing the above. Because if you do, you will have to restart your game. Break the bed near the medal for the potty.
Third potty is in Chapter 3. There is a bathroom that has two brakeable doors just down the hall near an exit from the sewers. Break the door on the right for a potty.
Potty number four is in chapter 5. In one of the buildings is a soldier with a request that you can pick up from his body. There is a building before the boss fight with some stamps in it where you can stamp his request to make it valiable. Return to the soldier and put request on his body. The potty will jump out. Pick it up. You should now have 4 out of 5
Last potty is in chapter 7. There are some containers that you can check in the beginning of the chapter. The potty is in one of them.