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Why is There Sewage Coming Up Through the Bathtub?

The plumbing system in your home is a complicated series of pipes that rely on gravity to take waste away from the building and send them to either a septic tank or the city sewer system. These pipes vary in size based on what type of fixture (bathtub, toilet, sink, etc…) they are providing drainage for. For instance, a bathroom vanity sink and a bathtub are piped with 1-1/2” piping, while the bathroom shower is a 2” pipe and a toilet is a 3” pipe. It all makes sense, right? The size of the pipe is based on what the drain is designed to take away. However, you may be asking yourself, then why would a bathtub be 1-1/2” pipe and a shower 2” pipe? Same stuff going down both drains, right? This is true, but the reasoning is pretty simple.

See, in general, a bathroom plumbing system consists of a vanity sink, a toilet and a shower or tub. These pipes eventually all tie together under the floor and ultimately all lead to a 3” pipe to take the waste waters to the basement and then outside of the home. Since all of these pipes tie together a clog in the drain line can affect all three fixtures. The first signs of a clogged drainage system could be gurgling, slow draining, poor flushing, and ultimately sewage backing up. Sewage is going to back up out of the lowest drain in that plumbing system which in almost all cases is the shower or bathtub. So, this is why homeowners will see sewage in their bathtub or shower before any other fixture in the bathroom.

Now we still need to answer the question of why a bathtub drain is 1-1/2” pipe and a shower is 2” pipe. The theory behind it is the 2” shower pipe is able to handle more volume which is important since there is less place for backed up water to go. While a tub can handle much more backed up water before the mess spills over onto the floor.

So, what do you do if you notice sewage backing up in your bathtub or shower? The answer is to call a plumber. Plunging will generally not prove to be an effective solution due to the multiple areas that the air, being forced into the pipe, can escape. Another initial thought might be a drain cleaning solution like Drano, this is also not recommended. For a slow drain this may help, but it can also rot pipes and make it dangerous for the plumber once they are ultimately summoned.

We have the tools, skill, and experience at Main Line Plumbing to clear your drains, determine the cause, and offer up solutions to prevent backups in the future.

You know who to call, Rochester


“We’re there when you need us”

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Jun 05

Understanding the plumbing system in your home can be complex. Different pipes handle waste from various fixtures like sinks and toilets. But why are some pipes different sizes? It's all about managing water flow efficiently. Plumbers ensure everything works smoothly, keeping your home safe and comfortable.

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