How to remove outdoor drain cover to clean insides and prevent overflow

One frequent cause of backups is that a root from a tree or large bush has grown into the pipe. If that's happened to you, you'll need to dig up the clogged area to sever the root and then repair the pipe, or if it's a porous drain pipe, wrap it in a landscaping fabric.

As Tester says, use a snake to see what you can find. You can also measure the distance until the snake gets stuck to get an idea of where you need to dig. Pay attention to any bends you feel the snake making on the off chance it isn't a straight run to the front.

Once you have an idea from one side, I'd fill the drain up with water on a dry day and see if you can find the outlet. Then try snaking from that outlet as well since the clog may be a long one from sediment building up over time. Again, measure the distance, and now you'll have an overall area to check.

First question: is the overflow blocked? If you fill up the sink and leave the water running, will it spill onto the floor?

If no, don't worry about it. There's may be some mold or soap scum in the drain. If that wigs you out, a bottle brush and some bleach should do the job.

Second question: is the drain blocked because your child pushed bits of toilet paper into it? If yes, then you'll have a solid mass of papier mache in the drain, and the only solution will be accessing it from the bottom (which means removing the tailpiece). My suggestion below won't help.

So, assuming that you have a "normal" clog in the drain, such as what might happen if you shave with a full basin and hair floats into the overflow, you can get a plastic mini-snake that is designed to pull hair out of a drain.

Here's one example that Home Depot sells: http://www.homedepot.com/buy/plumbing/drain-openers/brasscraft-zip-it-bath-and-sink-hair-snare-bc00400.html