Sans takes a sip of punch that's really more of a gulp. He has about half a dozen tiny umbrellas in his drink.

"Maybe you could get your own pool. If she's here," Sans says, with a barely there head tilt toward Marjorie, "then it's probably not against the rules."

Of course, Sans knows that with Papyrus, he's more likely to do the building himself. But considering what Sans has heard about vacuum salesman, it's probably better that Papyrus does the work himself rather than invites some weirdo over. At least part of this question is Sans trying to feel out Papyrus's reaction to it, measuring enthusiasm and excitement to further get a grip on how Papyrus is feeling.