One of the first things you might have noticed about "Toads" is that, when you read it aloud, (you should—really), it sounds very colloquial. That is, it sounds like the way people speak—maybe not in the word choice, some of Larkin's choices feel a little dated now, but the rhythm, the cadence of the lines, does sound like speech. "Just for paying a few bills!" and "No one actually starves" sound more like lines out of a movie or play than what we imagine lines of poetry should sound like. The result of this colloquial style is that we feel like the speaker is talking to us, the reader. It pulls us into the poem, makes us feel included. We love to feel included, don't you? Thanks, Phil.
Larkin uses some italicized words to add to the speaker's colloquial sound. A line like "No one actually starves" could sound several different ways without that italicized starves. With it, we know that Larkin wants the word emphasized, giving the line the exaggerated, almost comical tone of someone trying to make a point in a slightly dramatic way.
Another thing you might have noticed is bunches of repeated sounds. That's our pal alliteration for you. Take a look at stanza 3:
Lots of folk live on their wits:
Losels, loblolly-men, louts—
They don't end as paupers; (13-16)
Hear all those repeated L sounds? Alliteration can really make things sound musical and give the feeling that the words all belong together. In this case, all those folks that the speaker lists off as examples of people who "live on their wits" feel like they are part of one big team—they all have something in common.
What's that? You want us to sound off a little more about sound? Sure thing. Check out line 27:
Its hunkers are heavy as hard luck
Hear those heavy H sounds? With this alliteration, those heavy H's make it sound almost like the speaker is short of breath. It's like those heavy toads squatting on his life are making it hard for him to breath.
Lines 5 and 6 also use alliteration and consonance to make a distinct sound impression:
Six days of the week it soils
With its sickening poison—
What do all those repeated S sounds make you think of? Kind of hiss-y, right?—like Harry Potter speaking Parseltongue.
The sound repetition brings to mind snakes hissing. Snakes go along with that idea of something poisonous. True, this is a poem titled "Toads," and there are no snakes mentioned in the poem, but this hissing just adds another element of negative associations to the whole toad-work thing, reinforced throughout by the sounds of the poem.