We have a slow running shower drain so I went to our local hardware store and asked for a recommendation. He grabbed a bottle off the shelf and told me it works the best but it smells pretty bad. What an understatement. The bottle is labeled as "Virgin Sulfuric Acid". It states that while the product itself doesn't have an odor, the smell it generates when mixed with organic materials can be quite strong. The instructions are to pour in 8 oz, let sit for 15 minutes then flush with cold water for 5 minutes.
I poured it in, turned on the exhaust fan, closed the door and set the timer for 15 minutes. 10 minutes later, my wife came out of the bedroom and said "Wow...that stuff really stinks!". 5 minutes later we opened the door and literally, were almost knocked over by the fumes. Full on rotten eggs/sewage at an eye watering level. My wife immediately bolted for the downstairs and discovered that through the connectivity of plumbing, the fumes had spread throughout the house. I got the flush going and started flushing toilets and running water in sinks, hoping to get the odor moving out of the house. All the windows are open, fans are on and the "scent" still lingers. My wife is still outside an hour later!
Hopefully the drain is running faster.