The answer to 'why is my drain foul smell' is that a foul odor coming from a drain is often caused by a buildup of organic matter, such as food particles, hair, and soap scum. This can create an ideal environment for bacteria to thrive, leading to unpleasant smells. Common symptoms include a persistent, unpleasant odor coming from the drain, and the smell may worsen when the drain is used.
There are several potential solutions, depending on the severity of the issue. For minor clogs or odors, you may be able to address the problem with a DIY solution, such as using a drain cleaner or plunging the drain. However, if the problem persists or the drain is severely clogged, it's best to call a professional plumber. They can use specialized tools and techniques to thoroughly clean the drain and address the root cause of the problem.