The ones last time weren't too bad, so it depends on the size of the facility. I personally just prefer the relative certainty that a vent will get inside the facility, compared to the "if" with a sewer entrance.

[She's about average size herself, but she did see at least one person larger than her in the vents the previous time around, so the question is whether this facility has ones of comparable size. There's not a lot of point standing out here asking that question, though.]

If the patterns I've seen from the guards so far are any sign, there should be a vent clear for a few minutes shortly, so we can check properly.