Three-way diverter valve

Short definition

A three-way diverter valve is the manual or automatic switch in a greywater system that routes wastewater either to the reuse path (landscape irrigation) or to the sewer or septic. WAC 246-274’s failure-response requirement effectively makes it code-required for any compliant WA Tier 1/2/3 system. A simple manual ¼-turn valve costs $30–$100.

What it is

A standard plumbing tee splits one pipe into two — but always sends water to both sides. A three-way diverter valve has one inlet and two outlets, with a handle that selects which outlet receives the flow. In a greywater system, that means flipping between “send to landscape” and “send to sewer.”

The valve types:

• Manual ¼-turn brass or plastic 3-way valve — simplest; user-operated. The dominant choice for residential Tier 1 systems.
• Automatic sensor-controlled — advanced; rare in residential.

Sizing matches the source line:
– 1.5-inch for laundry standpipes.
– 2-inch for shower trap arms or larger drain lines.

Install:

1. Cut into the existing drain line at the source — laundry standpipe, shower trap arm, lavatory tail piece.
2. Route one outlet to the sewer or septic; route the other to the greywater system.
3. Place the valve in an accessible location (near the washing-machine outlet box is typical).
4. Label clearly — many plumbers add tags reading “GREYWATER” and “SEWER.”

Why it matters to a homeowner

WAC 246-274 specifies that if a greywater system fails or is suspected to fail, the owner must immediately divert greywater to approved sewer or on-site septic. The three-way diverter valve is the mechanism for that — without it, you can’t comply with the failure-response rule. That’s why it’s effectively code-required for every WA greywater system, even a small Tier 1 setup.

The diverter is also what makes seasonal operation practical:
– Summer — flip to greywater reuse, irrigate landscape.
– Winter — flip to sewer, avoid frozen distribution lines.
– Vacation — flip to sewer, no system to worry about.
– System maintenance — flip to sewer, work on the greywater path.

When a contractor proposes a “simple” greywater install without a clearly visible diverter, that’s a red flag. The diverter is the most basic piece of compliance hardware in the system. Budget $30–$100 for the valve plus install time.

Common failure modes

• Calcified valve in hard-water regions (Spokane, Eastside) — sticks in one position over time. Replace or service.
• User forgets to switch in winter freeze — greywater system overflows or freezes.
• Cross-leak across diverter — small bypass to the “off” position; usually inconsequential at residential scale.
• Brass body dezincification in chloraminated water (Seattle Cedar/Tolt water) — replace with DZR (dezincification-resistant) brass or PVC.

Common variants

• Three-way diverter valve (3 ports: in, out-A, out-B) vs. tee plus valves on each branch (functionally similar but more parts).
• Manual vs. automatic (sensor or programmable).
• Brass (durable but DZR consideration in chloraminated water) vs. plastic / PVC (cheaper, lighter; freeze-prone less of an issue indoors).