This is not a pretty post, but if I can help just one person get rid of the funky smell underneath their kitchen sink, it’s worth posting it.
Six years ago, when I moved into our fixer upper, we noticed a yucky smell coming from underneath the kitchen sink. We could only smell it when the AC was on, so only during hot summer months. It was a rotten egg, old food kinda smell. I tried everything. Baking soda,vinegar, hot water, essential oils, enzymes, even a plumber. He figured the smell must be from old food stuck in the pipes. Except when he checked, the pipes were clean so he couldn’t tell me what caused the smell.
Winter came and I forgot about it. This continued into 2020. During Covid-19, I had some extra time on my hands due to schools being closed, so I started digging for an answer. And I found it!
The culprit was an Air Admittance Valve. If you have one of these underneath your sink and it’s old and gross looking, you might want to replace it. Basically, the valve was old and cracked which let sewer gas seep through.
I found mine for $23. I unscrewed the old one, screwed on the new valve. The smell was gone instantly. I kick myself in the butt for not figuring this out six years ago. I guess better late than never.