First, here's what you don't do. Don't try to clear the clog with chemicals. They will not work and they will create a hazard for the professional that you end up calling. If you already have used something, tell the plumber what, when, and how much you used so he can protect himself from serious chemical burns. Next thing not to do is try a DIY snake. These are seldom large enough to do the job and frequently will make the clog worse. Professional equipment is dangerous to mess with as well even if you could find it. OK, now you might have already inferred where I'm going with this. Call a plumber that has the professional equipment and skill to properly auger the drain. We usually suggest you avoid companies that have "Rooter" as part of the company name. While some of these may be OK, many do not have the overall skill and equipment to do the job right.