How do I start cleaner job at the pub. ALways says Sammy doesn't have a change of clothes, and she doesn't want to spoil her own, regardless of the raggedy state of them.
Oskar gives you cleaning clothes if you offer to clean around the apartments. I have never tried this, but presumably you can use those if you only want to clean and not serve drinks. Otherwise, as has already been mentioned, the bar uniform does the trick.
ETA:
Ran a quick test, out of curiosity:
If you have the clothes from Oskar, you can use those for pub cleaning.
If you then get the Maid outfit, Sammy will switch to that instead.
Finally, if you start serving drinks in the evening, the pub outfit takes priority for cleaning.