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Plumb a New Basement Bathroom

Toilet installation

Plumbing a basement bathroom can be time-consuming and expensive. Here are a few of the potential problem areas, along with tips from experts, on how to do the job well.


Gravity usually isn’t on your side when building a basement bathroom. In many cases, you’ll need an ejector in order to transport waste away from the bathroom. However, sometimes the sewage lines will be far enough below the floor to allow you to plumb the bathroom without an ejector. (This is also dependent on local building codes.) Gauge the position of a sewage line by using a locator, and make sure the drainage lines are at least 4 inches in diameter for toilet and shower lines.


If the underground sewage line won’t work, you’ll need to excavate in order to dig the pit for the ejector. Concrete basement floors aren’t very thick, so you can cut through them with an electric jackhammer or saw. But before cutting, make sure you’re equipped to handle the concrete dust.

Build a plastic wall around the area and use a fan to blow the dust out of the house through a basement window.


When it comes to installing pipe, different municipalities have different preferences for material. But for most, there’s no question: Polyvinyl chloride (PVC) is the best. Because cast-iron pipe has pores like a person does, eventually acid can eat through the pipe.


Your next step is to backfill the area you’ve excavated. While it may make sense to fill the gaps with the same dirt you originally pulled out, that’s the wrong move.

Over time, after a few rainfalls and after the groundwater table rises and falls, the ground settles, leaving a void under the basement floor, which can be a source for cracks. Instead, use gravel, which allows groundwater room to seep without putting pressure on the floor. Add a sump pump (if there isn't one in the basement) for the same reason: The sump pump can protect the home from flooding and also prevent cracks from developing in the concrete patching.

Plumbing a basement bathroom can be a big job, but it’s not complicated once you understand the unique challenges. And that means more business for you, as more of your customers see their dream of a finished basement become a reality.

Project Information

  • Skill Level: Advanced

*Time and Cost are estimated.