Having a slow drain is an ongoing nuisance.  Once you have a slow drain, until the issue is properly addressed, the problem will only get worse over time.  If you ignore the problem long enough, you will end up with a clogged drain.  When you have a clogged drain, you have to drop what you are doing and fix the problem or call a professional plumber.  A professional plumber will do a great job for you, but having them clear your clogged drain is going to cost you.

A slow drain occurs when enough debris accumulates in a drainage pipe that it starts to choke off the pipe and restrict the flow of water.  The problem will tend to get worse over time because the drainage pipes will accumulate more and more debris until the material restricting the flow of water is removed.

Dealing with a slow drain first involves clearing the obstruction in the drainage pipe. Once that is done, you should start doing some preventative maintenance so that your drainage pipes keep flowing smoothly.

Flange plunger

Disclaimer: I am not a professional plumber, just a guy who has used different methods for fixing slow drains and wants to share his successes.  The methods should be safe, but use them at your own risk.