In the first episode of Peaky Blinders you find a scene where Grace Burgess personally applies for the job in the local bar/pub.
After discussing a bit with the owner whether she'll fit into this job or not, she starts to take up and empty pots from the floor into a bucket. The pots contain some 'mud-like' liquid. What was that and what was it good for? Did the bar visitors spit inside those pots, did they maybe urinate or puke inside?