try soaking it with the wet swab before rubbing too much, its really hard and wont come off until it has been softened. Is there just a small patch or is it stuck in the fuzz as well. If you could, post a picture.
If the poo is dried and covering the vent, cotton swab and water will be fine. It may take awhile to soften up and come off, that stuff is hard to get off. Keep at it.