Why Does Running the Shower Cause the Toilet to Bubble?

Although crucial to the proper performance of a house, the plumbing system is one of the least understood technologies used continuously throughout the day. Your plumbing infrastructure is comparable to the arteries and veins in your body. Fresh water is pumped through the house via water pipes so that fixtures like toilet and appliances can function and in so doing, this water gathers waste which is removed through an entirely separate system of pipes called drains.

These two lines are connected at the point of your plumbing fixtures and appliances. You can think of them as bridges that connect the two systems without contaminating the water supply. Turn on a faucet and you’ve activated the water line. The water falls into the drain line. Any appliance that used water has a system of inflow and outflow of that water.

What Makes Your Plumbing System Work?

Even though pipes and fixtures and appliances may seem like complicated operations, plumbing basics are very straightforward. The components are actually quite a few and the system runs on very simple physical laws.

Your plumbing is composed of:

  • Water feed pipes
  • Waste drain pipes
  • The air and gas plumbing vent

That’s about it!

Of course, you can also add into the overall system the fixtures that process water and waste (sinks, showers, toilets, dishwashers, garbage disposals, etc.)

What are the Physical Laws of Plumbing?

  • Gravity
  • Water pressure
  • Air pressure

But although none of this is rocket science, maintaining a properly functioning household plumbing system can seem complex and puzzling when something goes wrong. Knowing a few things about how gravity, air, and water interact in the plumbing lines makes it a lot easier to fix problems when they arise.

The Bubbling Toilet and Drain Back Up

If your toilet is bubbling, it is doing so because of a problem somewhere in the drain line. This is an issue that must be acted upon as it often is a progressive issue that leads to the complete loss of function in your bathroom and possibly a nasty backup of your sewer lines.

Although there are a few things you can do that may easily resolve this issue, finding the problem and fixing it is usually best left to the pros. Benjamin Franklin Plumbing has seen all the variations on what causes a bubbling toilet and knows the best way to resolve all of them. We’ve been there. What’s happening is that you have a drain line that is backing up water or air into the toilet because it has nowhere else to go. The typical underlying causes are one of the following:

Venting clogs. Vents, or vent stacks, are pipes that run from the drain line up through the roof. Their function is to allow sewer gases to escape and to allow air into the drain line so that flushing or draining the water doesn’t drag all the water out of the “P-trap” located at the ends of the drains for the tub, sink, and toilet. P-traps are designed to hold standing water which acts as a barrier against sewer gases and odors coming back up the pipes and contaminating the air in the room.

Because the vent is a straight pipe that emerges from the roof, it may get clogged by debris, insects, leaves, even dead mice. Most modern vents have a protective cover over them, but we’ve seen things get in there and clog the vent anyway.

When a vent is clogged it restricts airflow. Your house will have multiple vents, each of which sits over important junctions in the drain system. For example, a bathroom usually has a tub/shower, sink and toilet that flow into a common drain pipe that then flows into the main drain line. The vent stack will sit over that drain line.

Drain clogs. Somewhere in the bathroom drain line either close to the toilet or farther down the main sewer line there is a clog that is forcing negative air pressure back up the line. The first point of release is up through the toilet. The air or backed up water from what is sitting in the toilet will bubble.

Plumbing not done to specification. If this problem is occurring in a new build house or bathroom addition, there may be no vent or an incorrectly built vent (e.g. a portion of the vent running horizontally) or any number of wrong installation steps. Before you do anything else, get the plumbing work inspected by a professional plumber.

How Can I Fix This?

Try the simple solutions first. At any point, if you feel over your head, call us. We are here to help.

  • Eliminate the possibility that this is a clog at the municipal sewer line by checking to see if your neighbors are having the same issue. If so, call the city to have them fix it.
  • Duct tape over the shower/tub drain and sink drain and vigorously plunge the toilet. Because the other drains are sealed and cannot release pressure, the toilet water you are forcing through the drain line may dislodge a clog.
  • Check for clogs in the vent stack on the roof. If you have a number of vent stacks on your roof, look for the one that is roughly over the problem bathroom. If you only have one stack, it simply means multiple vents have been combined beneath the roof so that the roof is only penetrated once. You’ll need a thin flashlight securely tied to a thin rope to look down about 10 feet. If there is a clog near the top, you can remove it with a wire hanger. To ensure there are no clogs farther down the pipe, you can turn on your hose and pour water down the stack. Water hosed down a vent wash down and out through the sewer system.
  • If plunging the toilet didn’t work, the clog may be harder to dislodge or there is a clog further down the line. The real clue here is if you do or don’t have the same problem in other bathrooms, particularly ones on a lower floor. If this is the only bathroom with the issue, you will have to snake out the drain line that the bathroom fixtures are attached to. Start with the tub. If that doesn’t work, you will need to snake the toilet and may have to remove the toilet to do so effectively. We recommend calling Ben Franklin Plumbing at this point.
  • If the problem is a general one in the house, the clog is most likely in your outside sewer line and that line will need to be cleaned out. It is often due to root invasion in the pipe.