cleaning up someone else's mess; making up for someone else's mistake
Idiomatic use: taking responsibility for another person's failure or trouble, often reluctantly. Commonly used with する (e.g., 尻拭いをする).
I was made to clean up my boss's mess.
I'm tired of always having to fix his mistakes.
ass-wiping; arse-wiping
Literal meaning: the act of wiping someone's bottom. Rarely used in modern Japanese outside of explaining the idiom's origin or in very crude contexts.
Literally, 尻拭い means wiping someone's bottom, but it is hardly used that way nowadays.