Bucket

A bucket, also known as a pail, is a type of carrying equipment that is either shaped like a truncated cone or a vertical cylinder. Regardless of its shape, it was generally watertight, was open at the top and flat on the bottom, and was able to be carried by a semi-circular handle. Generally, it was used to transport fluids by hand for utility work.

Usage
In 1999, during the Zanzibar Land Disturbance, the FOXHOUND agent Solid Snake located and procured a solid metallic washbucket, which was meant to be used for cleaning bathrooms, in the men's restroom in the Zanzibar Building's fourth floor. He later made use of it to disguise himself and scout out for the former STB agent Gustava Heffner, who was disguised as a Zanzibar Land soldier, with her only clue to her identity being that she used the ladies room (as there were barely any female soldiers among the Zanzibar Land military forces).

Behind the scenes
The bucket is a procurable item in Metal Gear 2: Solid Snake. Although procuring the item is completely optional, the article assumes Snake did so.

"A metal bucket used for cleaning bathrooms, Looks pretty solid. Its use is unknown."

- Bucket description in Metal Gear 2: Solid Snake