The answer to 'why is my sump pump foul smell' is that a foul odor coming from your sump pump is often caused by stagnant water, debris, or bacterial growth. This can happen if the sump pump is not maintained properly or if the sump pit collects organic matter over time.
Some common causes of a smelly sump pump include: debris and sediment buildup, bacterial growth in standing water, and lack of regular cleaning. The sump pump may also smell if the check valve is not working properly, allowing sewage or wastewater to back up into the pit. In some cases, a faulty sump pump can also contribute to unpleasant odors.