The answer to 'why is my garbage disposal foul smell' is that a smelly garbage disposal is usually caused by food or debris buildup. This can lead to bacterial growth and unpleasant odors. Common symptoms include a rotten egg or sewage-like smell coming from the sink drain.
To fix a smelly garbage disposal, you can try some DIY solutions like running lemon or orange peels through the disposal, or using baking soda and vinegar to clean it. However, if the smell persists or the disposal is clogged, it's best to call a professional plumber to inspect and properly clean or repair the unit.