The first Plumbers' Badge is located on top of the awning to the right of the generator in the streets. Use Spidermonkey to climb up the drain pipe to reach the awning.
The next Plumbers' Badge is directly across from the one on the awning in a fenced in area. Spidermonkey is, again, the best character to reach this Plumbers' Badge.
The following Plumbers' Badge is in a dead end alley to the left after crossing the area with the downed power lines. Head down to the end of the alley and jump off of the nearby bench to collect it.
After making your way through the building and activating the switch to open the door, proceed down the hall to the set of elevators. Move to the far set of elevator doors that are partially closed and use Humungousaur to open them. Once the doors are open you can drop down and collect the next Plumbers' Badge.
The next Plumbers' Badge is on the ledge in the room with the movable block and switch that activates the laser grid on the floor. After activating the switch, transform into Spidermonkey and double jump onto the block and then onto the ledge to collect the final Plumbers' Badge in this level.