Depending on your caravan’s age and intended use, you will likely use one of two systems to store wastewater:

• Fixed Polyethylene Tanks: Usually grey in color to distinguish them from fresh (blue) or black (black) tanks. These are bolted to the chassis. Modern Australian-made tanks often feature 8mm thick walls, removing the need for heavy steel bash plates while protecting against stone chips.

• Portable “Totes” (Rolling Tanks): If your van doesn’t have a built-in tank, a wheeled portable tank is a common alternative. To meet CMCA (Campervan & Motorhome Club of Australia) self-containment policies, these must be connected to your outlet via a sealed hose and include a shut-off valve to prevent accidental spills.

Because grey water contains food scraps, hair, and grease, the fittings are larger and more robust than those used for fresh water:

• Wide-Bore Inlets ($1\frac{1}{4}$” or $40\text{mm}$): To prevent blockages from food particles, grey water plumbing uses wider pipes. Standard fittings often include a 40mm ball valve for the main outlet to allow for fast, “dump-and-go” emptying.

• The Sullage Hose: This is the flexible ribbed hose that connects your van to a campsite drain. Unlike fresh water hoses, these are not pressurized. Ensure you carry at least 5–10 meters and a “joiner” to reach distant drain points.

• Breather Vents: A grey water tank must have a breather (usually 13mm or 20mm). Without a vent, the air trapped in the tank will cause your sinks to “glug” and drain slowly, or worse, cause the tank to expand and crack under pressure.

The 24-Hour Rule: In the Australian climate, grey water can turn into “black water” (biologically hazardous) within 12 to 24 hours due to bacteria growth. This is why many National Parks and “Leave No Trace” sites require you to have a sealed, plumbed-in tank.

• CMCA SCV Policy: To be certified as a Self-Contained Vehicle (SCV), you must have a fixed, plumbed-in sink and a grey water tank (fixed or portable) that can be isolated with a valve.

• One-Way Valves (HepvO): Many modern vans replace traditional “P-traps” under the sink with HepvO valves. These are waterless valves that prevent grey water odors from coming back up the drain while you’re driving, without the risk of water splashing out of the trap.

• The “Boiling Water” Flush: When emptying your tank at a dump point, pour a kettle of boiling water down your kitchen sink. This helps melt accumulated grease and fats, flushing them out of the tank before they solidify and cause smells.

• Avoid “Donut” Seals in Parks: When connecting to a caravan park drain, use a rubber “donut” or threaded adaptor. This creates a seal that prevents smells and pests from escaping the park’s sewer system into your campsite.

• Filter at the Source: Use simple mesh sink strainers. Preventing hair and food scraps from entering your tank in the first place is 90% of the battle against grey water odors.

Always use designated Dump Points for emptying your tanks. If you are in an area where “ground discharge” is permitted, ensure you are at least 50 meters away from natural waterways and use biodegradable, phosphate-free soaps to protect the local ecosystem.