Liquid drain cleaners generally fall into three categories: alkaline (sodium hydroxide or potassium hydroxide), acidic (sulfuric acid), and enzymatic. Alkaline cleaners are best for dissolving hair and grease in residential bathrooms and kitchens, while acidic versions are typically reserved for professional use to clear heavy mineral scales or paper clogs. Enzymatic cleaners are the safest for long-term maintenance and septic systems, as they use bacteria to digest organic waste without damaging pipes.