Greywater System for Toilet Flushing: DIY and Kits

What Is Greywater and Why Use It for Toilet Flushing?

Across the United States, the average household flushes a toilet between 5 and 8 times per day per person. At 1.28 GPF on a modern EPA WaterSense-certified toilet such as the TOTO Drake II or Kohler Cimarron, a family of four still consumes roughly 18,000 to 24,000 gallons of fully treated municipal drinking water per year just on flushing. Replacing that volume with greywater offsets significant utility cost and reduces pressure on municipal treatment plants.

The concept is not new. Countries including Australia, Japan, and the United Kingdom have broad greywater reuse frameworks for non-potable indoor use. In the US, adoption has accelerated since California, Arizona, and Texas updated state plumbing codes to allow indoor greywater reuse under specific conditions. Understanding which source, which routing path, and which treatment level your system needs is the first step before selecting hardware.

Is Greywater Toilet Reuse Legal in Your State?

Before purchasing any kit or cutting any pipe, take these steps:

1. Contact your city or county building department and ask specifically about "indoor greywater reuse for toilet flushing" and whether a permit is required.
2. Check your state plumbing code (most are searchable online) for language around "non-potable water reuse" or "grey water."
3. If you rent, review your lease and consult the landlord -- most installations involve cutting into supply or drain lines, which requires landlord consent.
4. Verify with your homeowner's insurance that a permitted greywater system does not affect your water damage coverage.

In permitted jurisdictions, greywater used for toilet flushing must generally be held in a covered, opaque tank, piped in purple or clearly labeled "non-potable" conduit, and prevented from any cross-connection with potable water lines. These requirements align with the International Plumbing Code (IPC) Chapter 13 provisions adopted by many states.

How Does a Greywater Toilet System Actually Work?

The core components of any greywater-to-toilet system are:

• Diverter valve: Installed on the sink or shower drain line to redirect water to the storage tank rather than the main drain.
• Primary filter: Removes hair, lint, and particulate matter. Typically a mesh screen or sediment cartridge rated 100 to 200 microns.
• Holding tank: An opaque, sealed vessel (5 to 15 gallons for single-bathroom systems; 20 to 50 gallons for whole-house applications) that stores filtered greywater. Tank sizing is critical -- too small means frequent potable water backup; too large allows stagnation and odor.
• Pump or gravity feed: Gravity systems are simpler and cheaper but require the holding tank to be positioned higher than the toilet's fill valve inlet. Pump-assisted systems are more flexible in layout but add an electrical component.
• Float or level sensor: Monitors tank level and signals the backup potable water valve when supply is low.
• Backup valve / mains supply: An automatic fail-safe that switches to municipal water when the greywater tank is empty. This is a code requirement in virtually all jurisdictions that permit indoor greywater reuse.
• Non-return (backflow prevention) valve: Prevents greywater from entering the potable water supply under any pressure condition. This is non-negotiable from a plumbing code and public health standpoint.

What Are the Best DIY Greywater Toilet Flushing Setups?

Option 1: Bathroom Sink to Toilet (Gravity Loop)

This is the simplest feasible system. The bathroom sink drain is teed before it joins the main drain stack. A 5- to 10-gallon opaque HDPE tank sits under the vanity or inside the wall cavity. Greywater gravity-feeds through a 100-micron mesh filter into the tank, and a float-controlled supply line replaces the standard cold-water toilet inlet. When the tank level drops below 2 gallons, a float-actuated valve opens the potable backup supply.

Approximate DIY parts cost: $150 to $300

Skill level required: Intermediate. You need to cut and re-plumb PVC drain lines and connect a new supply line to the fill valve. If your toilet uses a standard 3/8-inch compression inlet (which covers most TOTO, Kohler, American Standard, Woodbridge, and Gerber models), the supply connection is straightforward.

Water savings: A family of two using the bathroom sink 4 to 6 times daily can generate 3 to 6 gallons of greywater, covering 2 to 4 flushes on a 1.28-GPF toilet. Actual offset depends heavily on hand-washing habits.

Option 2: Shower/Bath Capture with Pump-Assisted Tank

A shower produces 2 to 2.5 gallons of warm water per minute. Diverting shower drain water to a 15- to 30-gallon holding tank and using a 1/6 HP sump-style pump to supply the toilet fill valve is a higher-yield system. A timer or float switch activates the pump only when the toilet requests water.

Approximate DIY parts cost: $250 to $500

Critical note: Shower water typically contains body oils, soap, and shampoo residue. A 100-micron pre-filter is insufficient for a closed tank that may hold water for several hours; add a bio-filter media or enzyme dosing to prevent sulfide odors. Change or clean filters every 2 to 4 weeks.

Option 3: Laundry-to-Toilet

A front-load washing machine drain can be diverted mid-cycle to a 30- to 50-gallon outdoor-rated tank. This is best suited for a first-floor bathroom or basement toilet directly below or adjacent to the laundry room. Because laundry greywater contains detergent and lint, a two-stage filter (coarse mesh + cartridge) is recommended, plus regular tank cleaning to prevent surfactant buildup.

Approximate DIY parts cost: $300 to $600

Water savings potential: A single laundry load produces 15 to 40 gallons of greywater (depending on machine efficiency), enough to cover 12 to 30 flushes on a 1.28-GPF toilet.

Which Packaged Greywater Kits Are Worth Considering?

Here are the main system categories and representative product lines available in the US market as of mid-2026:

Compact Sink-to-Tank Units ($400 to $800)

These self-contained units install under a bathroom vanity. A built-in filter and small holding tank feed the toilet supply line directly. The Procter Machine (Australian-made, now available via US distributors) and Aquadam Greywater Convertor are two examples. These units are typically 4 to 6 inches deep, hold 2 to 5 gallons, and include the diverter valve, filter cartridge, UV sterilizer lamp, and backup potable valve in one cabinet. Installation time is 2 to 4 hours for a plumber; DIY for a competent homeowner is 4 to 6 hours. Replacement filter cartridges typically run $20 to $40 annually.

Whole-House Greywater Recycling Appliances ($1,200 to $3,500)

Units such as the Aquacycle 900 (used in commercial buildings) or the Pontos AquaCycle capture greywater from multiple drains, run it through multi-stage biological treatment, and store treated water in a 50- to 200-gallon cistern that serves all toilets on the property. These are installer-only products requiring professional commissioning, but they deliver the highest water savings -- 20 to 35 percent of total household consumption -- and are the route chosen for new construction or major renovations.

Rainwater and Greywater Hybrid Tanks ($800 to $2,000)

In climates with regular rainfall (Pacific Northwest, Southeast), a slimline cistern under a stairwell or in a utility room can accept both roof-captured rainwater and greywater from a shower. The potable backup float valve keeps toilet supply reliable during dry weeks. This combined approach maximizes non-potable water availability and is increasingly used in net-zero home builds.

How Much Water and Money Can a Greywater System Save?

Actual financial savings depend heavily on local water rates, which vary from $0.002 per gallon in low-cost rural areas to over $0.015 per gallon in drought-stressed metros like Los Angeles, Phoenix, and Las Vegas. At $0.01/gallon all-in (water + sewer), the same family of four saves $150 per year, cutting payback periods roughly in half. Many water utilities in drought-prone states also offer rebates of $100 to $1,000 for certified greywater installations -- Arizona's WaterSense partner utilities, Southern California Water Coalition member agencies, and several Texas Municipal Utility Districts have active programs as of 2026.

Choosing the Right Toilet for a Greywater System

Any toilet that accepts a standard 3/8-inch compression cold-water supply connection can be fed from a greywater tank. That includes virtually every widely sold residential model. However, greywater has slightly higher mineral and organic content than treated tap water, which matters for certain glaze coatings and internal tank components.

For a toilet paired with a greywater supply, the following considerations apply:

• Tank material: Porcelain or vitreous china tanks do not corrode from greywater exposure. Avoid plastic tanks with unsealed joints that can harbor biofilm.
• Fill valve: Rubber seals in standard fill valves (Fluidmaster 400A, Korky models) are compatible with mildly soapy greywater. Inspect annually and replace every 3 to 5 years -- the same interval recommended for normal use.
• Glaze quality: TOTO's CeFiONtect glaze and similar nano-ceramic coatings create a surface that resists mineral adhesion and biofilm, which is advantageous when occasional lower-quality greywater reaches the bowl. The TOTO Drake II, TOTO UltraMax II, and TOTO Aquia IV all carry this coating.
• Flush volume: Low-flush models (1.28 GPF) maximize the value of every gallon of greywater reclaimed. The Kohler Highline with AquaPiston flush, the American Standard Champion 4 (1.6 GPF), and the Woodbridge T-0001 are all highly rated for flush performance at or near EPA WaterSense thresholds.
• MaP score: A toilet with a MaP score of 800 grams or higher ensures solid waste is cleared in a single flush even when greywater occasionally delivers slightly less tank pressure than pressurized municipal supply. The TOTO Drake II scores 1,000 grams (maximum MaP rating); the Kohler Cimarron and Gerber Avalanche both exceed 800 grams.

For a comprehensive list of high-performing toilets that work well with water-saving systems, see our best flushing toilets guide, which covers MaP scores and efficiency certifications for over 40 models.

Step-by-Step: Building a Sink-to-Toilet Gravity System

This walkthrough covers a single-bathroom, under-vanity sink capture system feeding one toilet. It assumes a 12-inch minimum clearance under the sink and a toilet located within 6 feet horizontally with the tank inlet below sink drain level. Before starting, verify local code and obtain any required permit.

Materials List

• 5 to 8 gallon opaque HDPE food-grade container with lid
• 100-micron mesh strainer basket (inline, 1.5-inch slip fit)
• 1.5-inch PVC diverter Y-fitting with threaded port
• 1.5-inch PVC pipe and fittings (quantity depends on layout)
• Float-actuated diverter valve (potable backup) -- 3/8-inch compression
• 3/8-inch flexible supply line (minimum 24 inches)
• Tank lid with bulkhead fitting for outlet
• Non-return check valve (3/8-inch inline)
• Teflon tape, PVC cement, PVC primer
• Drill, hole saw (for bulkhead fittings)

Installation Steps

1. Shut off water and clear the area under the vanity. You will need space for the storage tank and access to the sink drain P-trap.
2. Cut into the sink drain pipe below the P-trap. Install the diverter Y-fitting. In normal position (default), water flows to drain. When you activate greywater capture, it diverts to the holding tank. Some systems use a continuous diverter rather than a manual one -- choose continuous-divert-with-overflow for maximum capture.
3. Run the divert line through the inline mesh strainer into the top of the holding tank. The strainer catches hair and soap residue before it enters the tank.
4. Install a bulkhead fitting at the bottom of the tank for the outlet. Seal with waterproof silicone on both sides of the tank wall.
5. Connect the float-actuated backup valve. This valve monitors tank water level. When the tank is adequately full, it blocks the potable supply. When level drops below the float setpoint, it opens the potable supply. Wire the float per manufacturer instructions (most use a simple mechanical float, no electricity required).
6. Install the check valve inline between the holding tank outlet and the toilet fill valve inlet. This prevents any reverse-flow into the tank from the potable backup supply, which would violate backflow prevention code.
7. Connect the 3/8-inch supply line from the check valve to the toilet fill valve. Use the same connection method as a standard supply line.
8. Test the system with plain water first. Fill the tank manually, flush the toilet multiple times, and observe that the backup valve activates correctly when the tank empties. Check all fittings for leaks.
9. Reinstall the P-trap and run the sink to verify greywater flows correctly into the tank. Check for any overflow or backup into the sink.

Maintenance Requirements and Long-Term Reliability

A greywater toilet system is not install-and-forget. Organic matter, soap residue, and mineral content in greywater create maintenance needs that standard toilet plumbing does not face. Establishing a maintenance schedule from day one is the difference between a system that performs reliably for a decade and one that creates odor problems or component failures within the first year.

Monthly

• Remove and rinse the inline mesh strainer. Soap scum and hair accumulate quickly; a blocked strainer reduces flow and can cause tank overflow.
• Inspect tank interior with a flashlight. A healthy tank should be clear to light gray. Dark coloration, slime, or strong odor indicates biofilm growth requiring immediate tank cleaning and filter replacement.
• Test the backup potable valve by manually lowering the float. The potable supply should open within 2 to 3 seconds.

Every 3 to 6 Months

• Empty and scrub the holding tank with a dilute white vinegar solution (1 cup per gallon of water). Rinse thoroughly before returning to service.
• Inspect the check valve and supply line connections for any mineral deposit or discoloration.
• If using a pump-assisted system, test the pump by running it dry for 10 seconds, then verify flow rate has not declined (a sign of impeller wear or clog).

Annually

• Replace filter cartridges (for packaged kit systems).
• Inspect the toilet fill valve and flapper for unusual wear or soap residue buildup. These parts are inexpensive to replace and should be swapped if any stiffness or discoloration is visible.
• Check that all labeled "non-potable" markings on pipes and the tank are still clearly legible. Many codes require permanent labeling.

For related guidance on toilet fill valve and flapper health, see our articles on replacing a toilet fill valve and replacing a toilet flapper. For water savings strategies that complement a greywater system, the how to save water with toilets guide covers dual-flush upgrades, displacement devices, and leak detection. If you are also exploring the best low-flush toilets to pair with your system, our best low-flow toilets roundup covers 1.0 GPF and 0.8 GPF models with MaP scores.