Now, before you call a plumber I'd like to make a suggestion. I've used this with very bad clogged drains with success; you will want to use this method on each drain going from the highest running drain to the lowest.
You'll need baking soda, vinegar and salt. Mix the baking soda and salt together (1 cup baking soda, 1 cup salt) and make sure to mix it well. Then, at the highest running drain poor this mixture into the drain. Then, follow up with 1 cup of vinegar and as soon as possible BLOCK the drain using a wet rag or something.
Note, you may see water come up from other drains in the house... THESE are the drains you'll also need to preform this task on. This is a cheap and eco-friendly way to try and solve your problem.
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