The main reason you should consider putting a cap on your vent pipe is to protect it from the debris that can get in during the storm and prevent animals from climbing in. On the other hand, you should always protect your roof vent pipe with a vent pipe cover.

Can you put a cap on a sewer vent?

You don't put rain caps on sewer vents. If there is a leak into your house it may be your roof jack.

What is the purpose of a vent cap?

A fitting which provides protection for the open end of a vent stack, soil stack, or waste stack; prevents objects from being dropped down the stack.