The answer to 'why is my drain slow draining' is that a slow-draining sink or tub is usually caused by a clogged drain. Common causes include hair, soap scum, food particles, and other debris building up in the drain over time. Symptoms include water taking longer to empty or the drain gurgling.
There are a few potential DIY solutions you can try before calling a professional plumber. First, use a plunger to try to dislodge the clog. If that doesn't work, you can try using a drain snake or auger to physically break up the blockage. Chemical drain cleaners are another option, but use caution as they can be harsh on pipes. If the clog is deeper in the pipes, you may need to call in a professional plumber with specialized tools to clear the drain.