If you want to keep birds and other critters out of a PVC vent pipe, you could have your dog guard the pipe, but there is a better way, according to Mike Simonsen of Black Diamond, Washington. In looking for a more practical solution, he quickly learned that the hardware store doesn’t sell a product to keep birds and critters out of a 3-inch HVAC pipe that exited the side of his house. Using a 2 inch x 6 inch board, a hole saw, and some hardware cloth, Mike rigged-up his own solution to screen the pipe, the details of which he shares in this blog.
Read the entire article here: How to Keep Critters Out of a PVC Vent Pipe