SarahHighTide

Ah yeah you're right, would have been more accurate to say it's right below the gunwales. I would happily swap the smell inside for smell outside tbh. But it's not getting the chance to get outside.

Ah I see your thinking. It's possible I suppose, but It's installed on the side of the gunwales and is covered with a plastic disc that I imagine is designed to keep water out. I think it's installed as instructed in the spec sheet. It's one of these: https://www.leesan.com/shop/1-1-2inch-thru-hull-holding-tank-breather-fitting-stainless-steel-90-degree.aspx Maybe more likely moisture from an overfull tank backing up through the vent pipe? I guess I'll know when I take the vent pipe off the tank fitting.

There is a thru-hull holding tank breather fitting installed on the gunwales. So the filter should be making the air vented outside smell better. But I think it's probably not venting properly due to the granules blocking up the pipe.

Hi RR, Just found this post when I discovered a disintegrated carbon filter in the vent pipe on my boat. Some of the granules have fallen down the pipe. So I've bought a replacement filter and length of pipe and am working up the courage to detach and replace the vent pipe. Fingers crossed it's not too messy and solves the problem. Thanks very much for posting about your experience.