Have you ever had a sink that that wouldn't drain properly? Sink drains are usually slow due to build up of hair and other debris at the drain assembly.
To unclog a slow drain, fill the sink with about 2" of water.
Use a wash rag or paper towel to plug off the overflow opening near the top of the sink.
Now place a cup plunger over the drain and push down and pull up until the clog is cleared.
Be sure you use a cup plunger and not a flange plunger for toilets.
Clearing a slow draining tub is very similar to the sink.
First, remove the strainer at tub drain and remove any hair and build up you may have.
Again, the best plunger for this is the cup plunger.
Second, remove the trip lever; this is the lever just above the drain that you use pull up to when you want to take a bath.
Take a wash rag or paper towel and plug off the opening.
Fill the tub with a few inches of water; take the plunger in one hand cover the overflow drain with the other hand.
Move the plunger up and down in a force full motion to clear the drain.
Repeat these steps several times until the drain runs clear.
Keep in mind that most clogged drains come from hair and soap build up.
There are several different types of strainers you could use that would help block some of this from going down the drain.