Sometimes, vigorous plunging can help you out, and sometimes chemicals can help (like Draino or Liquid Plumber), but other times a "professional" is needed. If you're referring to a toilet drainage problem, well sometimes your pipes get backed up for various reasons -- either because there's too much of something jamming the pipe, or there's something that shouldn't be flushed down there. If you're having problems with other drains, like sinks or something, you may be able to clean your trap out either chemically or by removing the cap and cleaning out the gooey stuff sure to be in the trap. Unfortunately, sometimes the problem is not in the immediate area of the drain -- ie its in the bowels (pardon the pun) of your plumbing. In this case, you should either hire a professional (RotoRooter, RooterMan, etc.) or if you're handy, you can get a home rooter and do it yourself. I wouldn't suggest the latter on an older home, though, because you could damage the pipes if you don't know what you're doing. When in doubt, you can always call your local plumber!