We bought a 1967 year old ranch 2 years ago and have been experiencing a foul smell coming from our bathroom sink. We have been putting bleach, vinegar and soda down the sink and overflow over and over again but the foul smell keeps coming back. What do you think the problem may be?
A blocked vent is probably the most likely culprit. Other things to consider: leaking plumbing from a low point in the trap under the sink letting the trap drain, evaporation of the water in the trap if this sink is rarely used.
Some sinks do not have a true vent, and may have in place aa AAV (Air admittance valves-AAVs or Durgo valves or Studor vents). In my experience, these are poorly designed and allow sewer gas to seep through.
Sometimes really old hair that has been in a drain pipe for a long time will smell pretty bad. Not a sulfur smell like sewer gas, but more like a poop smell.
Every sink with an overflow hole near the top that I used would start smelling bad. I tried everything but my sink was the only one in the house that would start to stink, even when we changed houses, so I knew I was the problem.
I have gaps between my teeth and I have to floss after each meal. I rinse my mouth in the sink and food particles get trapped in the overflow drain outlets in the the drain pipe below the sink. I removed the drain trap them used hot water and flushed the over flow at the top of my sink and could see gunk coming out of the overflow outlets in the drain.
I used toilet bowl cleaner in the same way and after that flushed with hot water again a few times till the overflow outlet had clear water only. The smell disappeared too. I have to repeat this every month to keep it smell free. I stared drinking water after flossing after each meal instead of rinsing in sink and now I have to clean the overflow every 4-6months.
I use a sink drain shroom so it’s easy to remove when I clean the overflow. I will move to a sink without an overflow when I can. I hope my experience helps someone who has tried everything else.