See, you're assuming they have sinks. Or kitchens.
Let's go down the list. Cows are, primarily, grass-eaters. Of course, they've also been demonstrated to have clothing and various wagons; this might imply that cow society is not a strict extrapolation of real cows. However, the wagons themselves seem to indicate a semi-nomadic lifestyle, eliminating the possibility for a permanent kitchen and by extension a sink. The deer live in cities that are generally created and run by the ice sprites; I expect that while they would HAVE kitchens, very few of the deer would actually enter them to see how they worked, and might associate sinks solely with opulent restrooms. Unicorns, like the deer, have a central living space; however, it is in a magically crafted forest, so a specific 'food preparation place' might not actually exist beyond 'there are fruit here to pick' and their sinks might merely be shaped leaves for rainwater repository. The alpaca, like the cows, are highly nomadic and again do not have the structures necessary for the kitchen or sink; furthermore, theirs is a society based off 'living off the land' and has few frivolities. The sheep... actually have cities, technically, which implies they do have kitchens, but their somewhat ditzy nature would make it hard for them to create and maintain the plumbing necessary for sinks. Our best bet would be the longma, who at the very least have armor and an empire; even then, their high temprature home would make it difficult to create plumbing, though not impossible.
Artwork by Evka-Isharma (DA)
