The answer to 'my hydro jetting smells bad' is that a foul odor from hydro jetting is usually caused by the buildup of organic matter, such as grease, hair, and food waste, in your plumbing system. This can create an unpleasant sewer-like smell when the hydro jetting process dislodges and flushes out these materials. The smell is typically temporary and should dissipate within a few hours or days after the hydro jetting service.
However, if the smell persists or is accompanied by other issues like slow drains or backups, it could indicate a more serious problem with your plumbing system that may require further investigation and repairs by a professional plumber.