In the crawl space beneath my house, the sewer line has a branch that runs right to the crawl space entry/vent. The end cap has a jagged hole:
Not sure if it's been that way since I bought it (recently). There are definitely signs of rodents nearby in the crawl space, and my guess is they made this opening. Am inclined to replace this rubber end cap with a hard PVC clean-out end-cap. But am wondering if there's a chance this is a makeshift vent by the prior owner? (And if it were, why not just remove the end cap instead of gutting a hole in it)?
What do you think? Thanks!