Larkin includes some pretty unpleasant sensory details and imagery in "Toads." He wants us to really feel, to experience, the speaker's distaste and disdain for the "toad work" he was to deal with nearly everyday. Larkin's word choice leaves use feeling kind of stinky and soiled by the end of this one. Thanks for nothin', Phil.
Line 2: No matter how you try to dress it up, the word "squat" is unpleasant. Larkin uses the verb in line 2. It isn't a pretty picture. Nothing looks good or glamorous squatting. What if we try squat's adjective form? You know Bob, real nice guy, brown hair, and he's kind of short and squat. Not great, right? The word even has an unpleasant sound. Say it a few times. Or don't. The bottom line: It looks unpleasant, it sounds unpleasant: it's an unpleasantness double whammy. It's no accident Larkin used this word so early in the poem. He wanted to get the ugly ball rolling right away so we would start experiencing the unpleasantness of the speaker's situation.
Lines 5-6: "Soils" and "sickening poison" are undeniably unpleasant in sound and association. All those S's make it sound like your hissing when you read these lines and hissing usually has negative associations: hissing cat, hissing snake. (Check out "Sound Check" for more.) And have you ever heard the verb "soil" used in a positive way? Probably not. Sickening poison is pretty self-explanatory. There just isn't a pleasant way to spin that phrase. Here again, Larkin wants to keep our minds and ears filled with unpleasantness so we can experience how our speaker is feeling about work and his life.
Line 15: Okay, we all know that fruit and fish are an important part of a nutritious diet. They are good things, right? Well, yes. But Larkin can make even these things seem kind of unpleasant. First off, the fruit is described as "windfalls." That means it is fruit that has been blown or knocked out of trees. In other words, it has been sitting on the ground and might be pretty banged up. Even if you get lucky and find a windfall in good shape, chances are it's surrounded by other pieces of fruit that have been on the ground much longer and have rotted. Not too appetizing. Now, on to the fish course. These folks aren't eating fresh caught Alaskan Salmon in a nice herb butter sauce. (Sorry, it's almost our feeding time.) These are "tinned sardines." Canned fish. To be fair, lots of people like sardines. But there is no denying that these little suckers pack a pretty powerful fishy smell that many folks find, you guessed it, unpleasant.