Toilet Backing Up Into Bathtub/Shower? Fix it Now!

Last Updated on August 3, 2023 by toilethaven

Why is My Toilet Backing up into My Bathtub/Shower?

It is one of those things that rarely happen, but when they happen, you almost don’t believe it. You flush your toilet, but instead of the waste flowing down through the drain to the city’s sewer lines, it backs up through your bathtub or shower drain.

If your toilet is backing up to your bathtub or shower, it is a sign that your sewer line is clogged. If you are on a septic system, it could result from a full septic tank. Since the toilet and the bathtub share the same sewer line, if it is clogged, waste from the toilet will have nowhere to go and back up through the tub.

Sometimes the main house drainpipe (also known as a drain stack) is clogged and not necessarily the sewer line.

But why would a bathtub/shower back up after flushing the toilet? Why doesn’t the waste back up through the toilet bowl?

To understand your house’s plumbing better, think of it like a tree. A tree has one big trunk and many branches. The tree truck in this scenario is the main house drain, while the branches represent each fixture’s drainpipe.

The main house drain line is then connected to the sewer line buried in your yard, draining the entire house’s waste to the city sewer line at the street or a septic tank.

When the main house drain or sewer line is clogged, the waste cannot flow out to the city’s sewer lines, and therefore the waste backs up through the drain with the least resistance.

If your toilet backs up your bathtub, turn off the water to the whole house and contact a licensed plumber immediately. Do not attempt to open the sewer cleanout or use chemicals to clear the clog. Sewer line clogs are best left to professionals.

The bathtub/shower drain has less resistance than the toilet drain. This is because the water at the bottom of the toilet, coupled with the design of the toilet trap, acts as a barrier.

If a toilet that backs up to the shower/bathtub is not fixed fast early enough, the waste will start backing up through all of the house drains, which could flood your house with sewage.

What Causes a Sewer Line/Drainpipe to Clog?

If your bathtub or shower backs up when you flush the toilet, almost always it is because your sewer line or main house drain is clogged. The drain could either be partially or fully clogged.

When the main house drainpipe is partially clogged, the bathtub/shower will back up then the water will drain slowly after some time. If it is fully clogged, the bathtub/shower drain will back up and not drain at all. You will therefore have a lingering and awful sewage smell in your bathroom.

But what causes the main house drain to clog in the first place?

1. Flushing objects that should not be flushed

It should never be flushed down a toilet if it is not liquid, human waste, or toilet paper. Too much toilet paper, however also responsible for clogging toilets most of the time.

Objects like toys, combs, diapers, feminine sanitary products, and hand towels, among others, have been pulled out of toilet drains so many times. Most of these objects, luckily, don’t make it past the toilet trap due to their shape.

Some of the objects, however, manage to negotiate their way past the toilet trap and into the main house drains, which causes a clog. Young kids are especially notorious for throwing stuff down the toilet, so if you have them in your house, you need to have a conversation with them about it.

2. Tree roots


Tree roots can extend quite far from the tree itself in search of water and support. Tree roots will naturally grow toward a water source as part of their adaptation.

If your house drain has a weakness or a small leak, the tree roots will patiently make their way into it and, with time, cause a major obstruction that will prevent your waste from flowing out, resulting in the toilet backing up in your bathtub or any other fixture in your house.

3. Mineral deposits

If you live in an area with hard water, then it is very possible that pipe scale will form inside your house drains as the minerals present in the water accumulate with time. The mineral mostly responsible for this is calcium.

Apart from your drains, the mineral deposits can clog your toilet bowl rim holes and siphon jet. If you, therefore, have a slow flushing toilet as a result of mineral deposits in the rim holes, you will also most likely have pipe scale in your drainpipe, resulting in a toilet backing up into other house fixtures.

4. Hair and Soap Scum

While showering, we lose some hair that is washed down the drain. Soap scum, especially in areas with hard water, can help to bind the hair together.

Although the main house drainpipe is quite wide, the drain will eventually clog when the hair and soap scum meets up with fats, oils, and grease from your kitchen sink.

5. Pouring Grease Down the Drain

Another thing that causes sewer lines to clog is grease. Grease will solidify inside the sewer line and form a clog that will restrict the flow of waste.

What is worse is that grease will combine with other substances in the wastewater, like calcium, to form a solid clog that is almost impossible to break down.

Most people believe pouring grease down the kitchen sink drain is ok, provided you follow it up with hot water. The truth of the matter, however, is that the grease will cool down, coalesce and form a clog.

What you should do after cooking using grease is to let it cool, then pour it into sealable bags and trash it. You can as well drop it in recycling plants.

How to Fix a Toilet that Backs Up into a Shower/Bathtub

You can’t live in a house where the waste backs up through the tub or shower drain every time you flush the toilet. You will need to fix it fast. The solution might be an easy one or a very complicated and expensive one, depending on what is clogging your drain.

You should start with the easiest solution and upgrade as the problem becomes more difficult to solve.

1. Turn off the Water to the House

The water backing up to your bathtub is contaminated with germs which can make you and your family ill. The first thing you need to do is secure the house by ensuring no more waste is backing up.

The way to do that is by turning off the water to the entire house. That means no one will shower, flush a toilet or run the washing machine or dishwasher.

To locate the main house shut-off valve, head to the basement and look for it very close to the water heater on the side facing the street. When you find the location, turn the wheel clockwise, but if it is a ball valve, turn the handle to be perpendicular to the pipe.

In some houses, the shut-off valve is on the external wall where the service line emerges from the ground. It will, however, always be on the side facing the street.

Do not forget to turn off the hot water shut off at the water heater as well. Remember, the water heater is still full of water.

2. Plunge the toilet

In this case, you will need 2 plungers—one flat-cup plunger to seal the bathtub/shower drain and another bell-shaped plunger to plunge the toilet.

The bell-shaped plunger is the best one to plunge a toilet since the bell will perfectly fit into the toilet bowl outlet. If you don’t have another plunger for the bathtub, you can try and be innovative. The idea is to seal off the shower/tub drain completely.

  • Have a helper seal the bathtub/shower drain with the plunger or anything else and press down firmly.
  • Flush the toilet and immediately start plunging. To plunge effectively, the bowl’s water must be high enough to cover the plunger cup. Flushing the toilet will also create more pressure in the drain.
  • Plunge aggressively and check if the situation is improving.

If you don’t seem to be making any inroads with the plunger, it is time to upgrade to a toilet auger.

3. Snake the Toilet


A toilet auger is a long flexible cable with a spring-like head and cranking handle that you push through your toilet drain to unclog. Most toilet augers are between 3 to 6 feet long.

Toilet augers have a plastic U-shaped protective guard that helps you prevent scratching your toilet while using it. Before inserting it through the toilet bowl outlet, pull the cable back until the auger head touches the guard.

Insert the auger head gently without touching the inside of the bowl and position the guard at the bottom of the bowl outlet facing upwards. Now start feeding the cable down the drain by cracking the handle clockwise.

When you come through a resistance, crack the handle in the opposite direction and clockwise again until you go past the resistance.

When the entire cable has been fully used up, pull it out by cranking the handle counterclockwise. Again remember to be careful with the auger head lest it leaves some very ugly marks on your toilet bowl.

If you go down with your toilet auger without resistance, the clog is way deeper in the drain.

 In this case, you may want to hire or borrow a longer motorized toilet auger. These augers can reach a distance of up to or more than 100 feet.

If you have never used an auger before and are not sure you will not scratch your toilet bowl, the best idea is to remove your toilet first. Removing and installing your toilet is fast and easy.

Another advantage of removing your toilet is that you can work on the drainpipe directly, which will be more effective.

If you decide to take this path, this is how to remove a toilet. Remember to buy a new wax ring since wax rings cannot be reused.

4. Call in an Expert

Sometimes despite your best efforts, you will not fix a toilet that’s backing up in your tub/shower on your own. Calling a professional plumber will help you quickly fix the problem, although it will be expensive.

A plumber will have more experience and sophisticated equipment. Sometimes they will even need to run a camera down the drain to see what’s clogging it specifically.

Most people will be tempted to open the sewer cleanout and see if they can clear the clog. Don’t try that.

If water is backing up from the bathtub, it means the vertical section of the pipe is full of raw sewage, which you do not want to flow out first from the cleanout.

You can hire a motorized auger, climb to the roof of the house, and snake the sewer line via the plumbing vent. Alternatively, you can pull out the toilet and snake the line from there.