The answer to 'bathtub foul smell' is that it is typically caused by a buildup of hair, soap scum, or other debris in the drain. This can lead to stagnant water and bacterial growth, resulting in an unpleasant odor. Common symptoms include a strong, sewage-like smell coming from the bathtub drain.
To address a bathtub foul smell, you can try a few DIY solutions first. Start by removing the drain cover and using a wire coat hanger or plumber's snake to clear any visible blockages. You can also pour a baking soda and vinegar solution down the drain, let it sit for a few minutes, then flush it with hot water. If the smell persists, you may need to use a commercial drain cleaner or call a professional plumber to inspect and clean the drain line more thoroughly.