My wife and I purchased our first home a few months back and have run into an issue that has prevented us from using our master shower. Shortly after using the tub or shower the shower starts to get a peculiar odor, my wife thinks it's mold and I think it's more of a moist earthy smell. We have a jetted tub, so I took off the side panel to scope out what I could. The smell inside is pretty similar to what the shower smells like, so I dug up the pipes a bit and and realized how terrible the previous owner was at DIY projects. My brother and I removed the tub and here's what we have - At the top is the tub drain + overflow, coming from the right is the shower drain, across from that is a "vent" that basically just ended in the open space under the tub (genius), and it all goes down into a shared p-trap that runs to the main drain. My best guess is when it all drains, it siphons musty air from under the tub and the air seeps into the shower. The main vent is about 6 feet down the line from this whole mess. We poured water down to check the p-trap, and it appears to drain smoothly. Do I need to run a vent up to connect it to the main, or can I block off the "vent to nowhere" and let the shower and tub use each other as wet vents? Or is this whole mess in need of an overhaul?