The best time to install graywater plumbing in your house is while the house is being built. That’s when you have easiest access to the space under the floor.
The second best time would be during a remodel or expansion, when the floor has been removed.
Here is a video showing how to install graywater plumbing for sinks and bath/shower under the floor of a house during a remodel. You’ll see the special fittings involved, special tools called for in this case, and the routing of the pipes for various options:
- Graywater out to a surge tank for use in the garden
- Graywater diverted to the sewer
- Graywater overflow from the surge tank back into the sewer when necessary
You can see that this kind of work is much more complicated than laundry to landscape. Because it alters the existing plumbing and ties into the municipal system, it requires a permit.
As involved as it is, it still follows the same core principles of any graywater system as laid out on our Build page:
- Use of a 3-way diverter valve
- Sloping the pipes 2% (1/4 inch of drop for each foot of run)
- Not storing greywater for more than 24 hours (in this case planning for a surge tank)
- Not shown here are the mulch basins in the garden where the greywater will be released below the surface
Backflow Preventer
One important addition here is a backflow preventer. As you see at 11:35 in the video above, if the sewer ever blocks up, the backflow preventer keeps the sewage from running back up the pipes and into the surge tank or into the sink and bath drains inside the house. When you connect your graywater plumbing to the municipal system, you need this kind of isolation cutoff.
Professional Installers
In this case, the installers are a professional company hired for the job. But if you study the video closely, you may decide you can do it yourself after all. The core principles are always the same.
However, it may be a matter of legality – see our Legal page, and check with your local jurisdiction, whether it’s the city, county or state. Bring your carefully thought-out plan when you apply for your permit, and ask about special situations, like the need to core-drill through the foundation as in this video. That might be something that requires a contractor’s license where you are. You don’t want to accidentally compromise the structural integrity of your house.