Bowser's pump works is located inside bowser's esophagus In in Mario & Luigi: Bowser's Inside Story. It is accessible when bowser defeats the blooper statue and drinks from it in plack beach.
Drinking the water as bowser floods the area, causing bone thwomps to rise, allowing access to other areas in the esophagus. While the esophagus is filled with water, Mario and luigi can float up to higher ledges.
Mario, luigi, and starlow investigate this area looking for princess peach. instead, they find toadsworth. ggez.
The area has 10 attack puzzle pieces that unlock a special fire flower attack.Also, it has an obstacle (a cannon that launches food for a giant Chombone) that is required to obtain the Stingler, an item that can be used to open the exit door resembling DNAs and access other areas of Bowser's body.