If a drain has not been used for quite some time the water in the p trap can evaporate and cause sewage odor to escape.
P trap sink smell.
The p trap is designed in a way that allows it to prevent the emission of sewer smelling gas into your residential area.
Run water down the sink drain at least once a month to prevent the trap from drying.
If the sink is in regular use you can eliminate evaporation as a cause of the smell so it is either blocked or there is a leak preventing the water from getting to the bottom of the trap.
There is a small amount of water in the p trap that blocks sewer gas from escaping as shown in the picture below this can cause your drain to stink.
Sewer gas smells and p traps every plumbing fixture and plumbing drain has a p trap on the drain if it is installed according to code.
If it fails at either one of these duties the result could be a smelly sink drain.
If the p trap is blocked or dry it would cause a sewage smell to emanate from the sink.
Underneath your bathroom sink there is a p trap.
Like many others your sink probably has a hole at the top that allows fast drainage when the sink is full of water.
These p traps protect us from sewer gas.
When the vents are blocked flushing a toilet can create sufficient vacuum to suck water out of the trap and allow sewer gases into your home.
A rancid odor coming from your sink drain may just be coming from debris in the p trap but if it smells like a sewer it probably means venting problems in your drain system.
Refill your p trap sometimes the musty smell coming from your bathroom is related to a dry p trap.
Pouring 5 teaspoons of mineral or vegetable oil down the sink drain can help prevent the water from evaporating as quickly.
Its job is to trap debris before it creates a clogged pipe and to block sewer gases from entering your home through the sink drain.
Cleaning out the p trap.
The p trap is the rounded pipe segment underneath your sink.
Inside the drain there is some water that is trapped there.
Smells emanating from the bathroom sink could be the result of bacteria growth on hair soap and other bathroom waste and if so cleaning the p trap and pouring baking soda in the drain are.
Sometimes it happens that the sewer smell in the bathroom comes from the sink.
If the p trap is not vented correctly this could be the potential cause of the sewer smelling gas in your bathroom.
The u shaped pipe is designed to hold water to prevent rodents from entering the house as well as keeping sewer gases from coming up out of the drains.