A slow drain is usually a buildup of hair, grease, and soap. Most clogs clear with simple tools, and you can avoid the harsh chemical drain cleaners that damage pipes over time.
Start with a plunger
A cup plunger works on sinks, tubs, and showers. Block any overflow opening with a wet cloth so you get good suction, add enough water to cover the plunger cup, and plunge firmly several times.
Clear the trap or use a snake
Under a sink, the curved P-trap catches debris and unscrews with a bucket underneath to catch water. For deeper clogs, a drain snake (auger) reaches into the pipe to break up or pull out the blockage.
Try hot water and baking soda
For grease and light buildup, pour baking soda followed by vinegar, let it fizz, then flush with hot (not boiling, for PVC) water. It's gentler than chemical cleaners and safe to repeat as maintenance.
When it's more than a clog
If multiple drains back up at once, or you hear gurgling and smell sewage, the problem may be in the main line — tree roots or a collapse — and needs a plumber with a camera and powered auger.