Question: Our shower/tub is not draining well. When water is running or draining the toilet next to it won’t flush, it backs up. Both make a gurgling sound when attempting to use the other. For example, when using tub, the toilet gurgles and bubbles. House and plumbing built in 50′s/60′s. Please help? Have tried using ‘Thrift’ in shower drain and flushing with hot water. No help.
Answer: The gurgling sound tells me that you could possible have a clogged vent. Both the tub and toilet will share the same vent. What you’ll need to do is go up to the roof and check for something blocking you vent stack. Birds will sometimes nest in these.
Have you by any chance recently had a new roof put on? Roofers are notorious for covering vents with a piece of shingle. A clogged vent is the same as placing your finger over the top of a straw and picking up liquid from a cup. No air flow? No fluid flow!
The only reason that I am suggesting a vent is because the problem only occurs in one particular room. Now, if it is a whole house clog, that is a totally different solution.