When filled, some grass or leaves are put on top of the water to prevent it Slopping over.
"Australia Twice Traversed, The Romance of Exploration Australia Twice Traversed. The Romance Of Exploration, Being A Narrative Compiled From The Journals Of Five Exploring Expeditions Into And Through Central South Australia, And Western Australia, From 1"
Ernest Giles
The wind was against me, and the beasts were incessantly trying to turn and rush back to the place they had been taken from, and the fight with wind and cattle went wearily on, the driving rain gradually soaking through my woollen poncho, theft through my clothes to my skin, and trickling down until my long boots were full and Slopping over at the knees.
"Far Away and Long Ago"
W. H. Hudson
He couldn't even keep his socks from Slopping about over his shoes.
"The Rough Road"
William John Locke