What this is and why you NEED one!
I've been using this tool, it's called a Zip It, I found this particular one at Home Depot for about $2.50 but I'm sure you can find something similar anywhere. You just take out the plug for the drain and stick the Zip It down in the drain and fish around for whatever is clogging it or slowing it down. It is really disgusting but it works, I'm actually kind of obsessive about it so I go around the house and clean all the drains quite often (I know weird right?), I figure doing preventative maintenance will reduce the chance of a big clog way down in the pipes where I can't reach. The package says for "one time use" bahhhh....I'll use mine until it stops working, I just clean it after I get done using it.
Here's a couple different kinds I found on Amazon, they are all basically the same thing ranging in prices, it's a long plastic stick with a handle and little barbs to hook whatever is clogging the drain, you don't need the most expensive one, mine was super cheap and it still works.