Stanza 3 Summary

Get out the microscope, because we’re going through this poem line-by-line.

Do they live in the station?

This line gives us a good reminder of the speaker's relationship to the station and its family. She's an outsider, looking in on these people. She's as in the dark as we are.
So she's got to do a bit of speculating here. Notice we have a question mark to add to our collection of cool punctuation. Our speaker addresses us in a way that makes us feel like we are right there with her (kind of like the very first line of the poem), and she's asking us to make some guesses right along with her.
By saying "they" the speaker excludes herself from them. There's no "we" relationship here.
This line also shows us how curious the speaker is. The poem has already gone through great lengths to highlight the filthiness of the place, and now it's taking a small turn to the interest in the people who populate the filling station.
But what's prompting her to ask this question in the first place?

It has a cement porch
behind the pumps, and on it

Here we are peeking into the lives of the people who run the filling station.
It turns out the speaker has guessed that these folks live at the station based on a few details she's spied with her Nancy Drew style sleuthing skills.
There's a porch—a sure sign of life outside of work. Porches are for chilling out and chatting with friends and family in the outside air. It's a cement porch though, which isn't exactly the coziest, but it might help cool things off when it gets really hot.
In these two lines, our speaker shows us how the family's work life ("the pumps") is connected and tied to the home life ("a cement porch"). The balance between work life and home life seems important in this poem, so let's pay attention and see if it comes up again.

a set of crushed and grease-
impregnated wickerwork;

On that porch is a set of dirty, grimy, greasy wicker furniture.
Here's another interesting mash up of something homey and something greasy and gross. Wicker furniture definitely rings "home sweet home," but in this case it's all grimed up, to the point that we're not even sure we'd want to sit on it.
The poem is collecting evidence of home life, but so far it doesn't look quite like the Brady Bunch lives there.
"Grease-impregnated" is yet another way of describing just how dirty things are. The phrase literally means full of grease, but the word "impregnated" makes us think of babies, and babies make us think of family. Slick moves, Liz.
We also feel slightly uncomfortable thinking of babies (which are soft and smell nice) in a world as grimy as this. It seems like an odd place for family living.

on the wicker sofa
a dirty dog, quite comfy.

Here we get more specifics about the filling station and the family: they own a dog. Aw, how domestic.
The dog, of course, is dirty too. No surprise there.
Dogs are another sign of home and comfort. And Bishop mentions that he's comfortable, which is a nice little break from all the uncomfortable grit.
It seems that even though this domestic scene is very dirty, it's comfortable being dirty. It's okay with itself.