There are few sites which recommends to use different methods of unclogging the drains; sinks and tubs drain. Don't do that. Call a plumber! You have 99% chance to make more damage in the drain. Most of the plumbing companies will came for free estimate. Ask when the plumber will be there as many question as possible. YOU DECIDE AND ONLY YOU if you want to pay for service! Don't use backing soda! That's madness! Be smart!