Gifford glosses the "exposed corporation emergency dustbuckets" that Bloom apparently is mentioning to Stephen at the beginning of Ithaca as "Outdoor trash baskets to be provided by the Dublin Corporation. This is one of Bloom's 'civic self-help' ideas; the baskets did not exist in 1904." But the strange use of the word buckets may show Bloom subconsciously hearkening back to some shameful hallucinations in Circe.
If Gifford is correct about the trash baskets, it absolves Bloom of one venial civic sin: throwing away the paper "throwaway" in the River Liffey, in Lestrygonians. Littering can hardly be condemned when a city provides no receptacles for its citizens to dispose of their trash. (And indeed the urban Liffey was a sea of floating trash at this time.)
But the word "dustbuckets" does not seem quite right for a trash basket. Buckets usually hold liquids, and that is true of nearly all the two dozen or so times that buckets are mentioned in Ulysses: they hold holy water, wet sand, beer, cleaning fluids, plaster, internal organs of butchered animals, mutton broth, street muck. The word dustbin was commonly used of household trash cans in the 19th century, and public trash cans in Dublin today are called rubbish bins, so why does Bloom think of buckets rather than bins?
Calling them "emergency dustbuckets" is even stranger, since throwing solid waste in trash cans is seldom an emergency. It seems possible that Joyce, in this chapter of Latinate words, is playing on the etymological root meaning of the word. Latin mergere means to immerse, to plunge into liquid, which confirms the impression that buckets should hold liquids.
Buckets do indeed perform emergency functions of receiving liquid in the book. In Circe a woman, feet spread wide apart, "pisses cowily" in the street, prompting a hallucination in which a "Gaffer" tells a story of a workman named Cairns who comes down from a scaffold in Beaver Street and "what was he after doing it into only into the bucket of porter that was there waiting on the shavings for Derwan's plasterers." Those listening to the story laugh loudly, which makes Bloom defensive (even though he is not Cairns): "Coincidence too. They think it funny. Anything but that. Broad daylight. Trying to walk. Lucky no woman."
Slightly later in the same chapter, Bloom is questioned in court about a still greater impropriety involving a bucket: "The crossexamination proceeds re Bloom and the bucket. A large bucket. Bloom himself. Bowel trouble. In Beaver street. Gripe, yes. Quite bad. A plasterer's bucket. By walking stifflegged. Suffered untold misery. Deadly agony. About noon. Love or burgundy. Yes, some spinach. Crucial moment. He did not look in the bucket. Nobody. Rather a mess." Still later in Circe, King Edward VII appears holding "a plasterer's bucket on which is printed Défense d'uriner" (Urinating Prohibited).
When Bloom thinks of dustbins, he may be subconsciously recalling the "emergency" functions that an "exposed" bucket might serve.