Do not use chemicals. They won't clear the clog, but will create a serious hazard for the plumber you should call. This is not a DIY job. It will require a professional with professional tools and knowledge on using those tools. Do not even consider renting a large auger. These are extremely dangerous in the hands of an untrained person. Find a "real" plumber who does not have "Rooter" as part of his business name. This is a time to bite the bullet and pay the man.