Ok, My house is pretty old, both my bathtub and toilet drain into our septic tank. Any time water drains out of our bathtub the toilet starts bubbling and when it stops bubbling the water stops drainging and takes a very long time to empty out and we can't flush our toilet during this time. But we can flush our toilet all day long and never have any backup problems till water drains in the tub. HELP ME!! Before I go out of my mind!