When plumbing smells like rotten eggs, there could be a serious sewer gas leak in your home. If this is the case, then do not ignore it. What causes this problem?
Drain not used in a while. Drain lines have a trap, which is a U-shaped pipe that contains water, and it stops sewer gas from coming up into your home through the drain. If the sink is not used for a while, the water in the trap can evaporate, leaving the unpleasant gas into your home. This can be fixed by running the water to refill the trap and get rid of the smell.
No drain trap. If a proper trap was not installed, this is likely to make that nasty smell. Nothing is blocking the smell from the sewer from entering into your home. If there's no drain trap, call a qualified plumber to install the proper trap.
Greasy drain. In many cases, grease or fat getting stuck in your drains causes the rotten egg or mouldy smell in the kitchen sink. When you pour grease down your drain, it can harden to the sides. As it starts to decompose the smell can make its way back into your home. To get rid of the smell, you can try putting a couple of teaspoons of baking soda in the drain and then pour in some vinegar. Then follow it with a pot of boiling water. The combination of baking soda/vinegar will eat away at the grease in the drain and the boiling water helps rinse it all away and clears the drain.
Clogged plumbing vent. Clog in the plumbing vent can cause the sewer smell back up into your home. Also, inspect the vent for blocking elements like a bird’s nest. Removing any obstructions and adding screens in the plumbing vents prevents future problems.