Why does my kitchen sink still smell like sewage after cleaning the P-trap?

Nine times out of ten, that smell is actually coming from the **basket strainers** themselves rather than the pipes you already cleaned. Check if you have the style with a plastic underside. There is often a tiny, hollow gap between the metal strainer and the plastic housing where old food and stagnant water get trapped. Since that area isn't part of the main flow of water when you're rinsing things, the gunk just sits there and rots. You can't really get a brush in there to clean it, so if they're slimy, you probably need to replace them with solid stainless steel units.

You should also check your **dishwasher drain hose** for a high loop. If that hose isn't pulled up and fastened to the very top of the cabinet underside before it connects to the sink drain, dirty sink water will constantly backflow into it. Those corrugated hoses are notorious for holding onto grease and organic matter. If you pull the hose off the connection and it smells like death, you’ve found the source. Installing a high loop or an air gap will prevent that backflow from happening again. Look at the slope of the horizontal arm connecting the two basins. If it's perfectly level or back-pitched, even a tiny bit, water will sit in the bottom of the pipe and turn into a layer of black sludge. Everything needs a slight downward pitch toward the P-trap to stay self-scouring. And if your husband cleaned the trap but didn't check the pipe going into the wall, there could be a thick layer of buildup further back in the sanitary tee.

Finally, check the height of the drain where it exits the wall. If the wall connection is lower than the trap, you might be creating a siphon that pulls the water out of your P-trap every time you drain a full sink. Without that water seal, **sewer gas** can drift right back up through the pipes. If you find the trap is empty after you haven't used the sink for a bit, that's exactly what's happening.

The strainer advice is solid, but one thing that gets overlooked is the Air Admittance Valve (AAV) if you have one under there. Those Studor vents have a rubber seal that eventually fails or gets stuck. If it's gunked up, it’ll let sewer gas leak directly into the cabinet space even if your trap is working perfectly. Look for a small plastic cylinder on top of a vertical pipe behind the sink; if it smells like a swamp right at the cap, you just need to unscrew it and twist on a new one.

I'm super new to this and honestly half of those terms sound like a foreign language to me lol. One thing I've been wondering though—does the sink have a garbage disposal? I've read that the black rubber splash guard can get realy slimy underneath and smell like a swamp if it's not scrubbed.

Is it hard to take that part out to check? I'm trying to learn more about plumbing so I don't have to call a pro for every little thing, but I'm worried about breaking somthing if I poke around too much!

I'm a bit skeptical it's just gunk in the pipes if your husband alredy cleaned them out that thoroughly. Have you ruled out a slow leak behind the cabinet floor? Sometimes the seal where the pipe goes into the wall fails, and you get stagnant water sitting on the subfloor. It smells identical to a drain issue but no amount of pipe cleaning will fix it.

Also, check the faucet base. If that gasket is old, every time you splash water, it's dripping behind the sink and rotting the wood. Is the bottom of the cabinet acutally bone dry to the touch?

Check the internal baffle inside that center-outlet tee. If you’re using a standard Oatey or Dearborn 1-1/2 inch setup, that plastic diverter can catch hair and grease like crazy if it’s slightly misaligned, creating a wall of sludge you can't see from the outside. Also, if you’re running an InSinkErator—specifically a Badger 5 or an Evolution—pull the discharge elbow off the side. Those rubber gaskets, like the #10082 flange gasket, get slimy and start weeping sewer gas long before they actualy show a visible water leak. While you're at it, toss those cheap clear poly washers and swap in some Dearborn Hi-Temp blue ones to ensure a gas-tight seal on the slip joints.