If your bathtub is filling up with waste water when you run water down any nearby drain, most likely you have a frozen sewer pipe, also known as waste lines, especially if your temperatures have been consistently cold. If you want to know why your waste lines froze, you can learn more about that here.
Most people who experience a plugged sewer or waste line, first call the roto-rooter guys. If you call them, ask if they work on frozen waste lines. Many do not and will charge you a service call to come out and tell you to call someone else because your sewer pipe is frozen.
Most people will try plunging the drain hoping to break it loose. If you plunge, plunge with care and only do it a couple of times. Plunging can cause the seal underneath your toilet to blow and may also blow apart p-traps. So keep plunging to a minimum or don’t do it at all.
Pouring hot water into your tub drain will probably have a minimal effect unless it’s only the tub drain that’s frozen. Drain cleaners will also not thaw a frozen waste line. The best way to get your sewer flowing again is to directly attack the frozen pipe from underneath the home.
Thaw Using a Torpedo Heater
I prefer to thaw frozen drain pipes with a torpedo-style heater (as pictured). They can run on propane, diesel, or kerosene depending on the model. Always run these heaters from outside the home (not underneath) and stand nearby every minute they are running. Locate the frozen sewer pipe and enclose the area around the pipe with cardboard or some other easy-to-position insulator. Enclosing the area will help concentrate the heat on the pipe so you don’t have to heat the entire crawl space to thaw the pipe. Then run your heater until the pipe has thawed.
If your pipe is really long, you may have to start thawing at the end that drops into the ground (the lowest point.) When that section is thawed, work your way back. You can tell when an area is thawed because the sewer pipe will be much lighter when lifting or moving it. Once the pipe thawed enough so the water starts to drain, turn on a faucet and let the water run until you don’t hear any more ice scraping inside the pipe.
If your frozen sewer pipe is fairly easy to access and you don’t have a heater, then you could cut out the pipe, thaw or buy new, then put it back with rubber Fernco couplers. Drain pipes should never freeze — and if they do there’s always a problem. Once thawed, correct the problem as described in this article. If during the process you noticed water leaking out from the bottom of a toilet, you’ll also need to replace the wax ring underneath that toilet.