It’s easy to imagine putting a bathroom in your basement remodel. It’s harder to figure out how to get waste and sewer gasses out.

Just like bathrooms in other parts of your house, adding a basement bathroom means wastewater must drain to the existing city sewer or to an on-site septic system, and sewer gasses must be vented directly to the outside in compliance with building codes.

Create falling waters

In most basement bathrooms, you must create “fall,” or you must give the waste a push.

All this pushing and falling costs money: Adding a basement bathroom could add $10,000 to your basement retreat budget.

 Wastewater from your basement bathroom sink, shower or tub, and toilet must have enough slope (another word for “fall”) to drain properly and effectively.

Achieving proper fall may require removing and rebuilding a small section of the basement slab and excavation of the ground underneath. The process involves digging a trench for a drainage pipe to connect the new bathroom to your home’s existing sewer or septic system.

Installing basement toilets

To give gravity an extra push, install a pressure-assisted toilet ($150 to $800) with a pressure valve that forces waste through the pipes and into your existing sewer line. This pressure assist may help you avoid digging into the foundation and creating a host of other hassles when adding a basement bathroom, including leaks.

If possible, locate the toilet (and other water-using appliances, such as a clothes washer) against an outside wall when adding a basement bathroom, which saves pipe and reduces the cost of draining away waste and venting sewer gasses.