Van Grey Water Systems

What Is Grey Water in a Van Conversion?

Grey water is wastewater from your sink, shower, and washing machine — anything that goes down a drain except toilet waste (that's called black water). Grey water contains soap, food particles, and dirt, but it's separate from black water because it's easier to manage. Some campgrounds and dispersed camping areas allow you to dump grey water directly (though not all), while black water always has to go to a designated dump station.

In a van, grey water goes from your sink drain and shower into a tank under the vehicle. When the tank is full, you drive to a dump station and empty it. It's not complicated, but the system has to be sized properly and designed so it drains completely.

What Size Grey Water Tank Do You Need for a Van?

Grey water tank size should roughly match your fresh water tank size. If your fresh water tank holds 40 gallons, your grey tank should hold 40 gallons too. Why? Because all the water that goes in comes back out — minus a little that gets absorbed in cooking, drinking, or watering plants.

Typical Tank Sizes

Most vans use 30-50 gallon grey water tanks. A couple taking one shower a day, washing dishes, and doing basic hand washing generates 25-30 gallons of grey water daily. So a 40-gallon grey tank fills up every day or two during active use. Larger tanks (50+ gallons) are useful if you want longer intervals between dump station visits, but they're heavier and take up more space.

Some people try to skimp on grey tank size to save weight or space. This is a mistake. A tank that fills up too fast means you're driving to the dump station constantly. The extra weight of a larger tank (about 8 pounds per gallon) is worth the convenience.

Tank Materials

Grey water tanks are plastic, just like fresh water tanks. They're typically thicker plastic because grey water is heavier and the tank gets jostled more (grey sludge sloshes around). Food-grade plastic isn't necessary here since it's not for consumption, but the tank still needs to be durable and UV resistant.

Should You Use Gravity Drain or a Pump for Grey Water?

Getting grey water from your sink and shower into the tank requires either gravity (the tank is lower than the drain outlets) or a pump (the pump pushes water downward into the tank). Your choice depends on where the tank sits relative to your interior fixtures.

Gravity Drain

Gravity drain is the simplest. If your tank is mounted low under the van and your sink and shower are above it, drain lines can flow downward by gravity alone. No pump needed, no electricity used, fewer components to fail. Most standard van conversions use gravity drains because the tank sits under the floor and all drains are in the raised interior.

The catch is that you need continuous slope — the drain line has to consistently descend from the fixture to the tank. If the line flattens or rises, water collects and things get smelly. We slope drain lines at least 1/4 inch per foot, and we avoid loops or dips where water can pool.

Pump Drain

If your tank is mounted high or inside the van (some people put it under a bed), water needs to be pumped down into it. A grey water pump is usually a small submersible pump in the tank that activates when water enters, pushing it upward into a drain line that returns to a higher tank. This is less common in vans because it uses electricity and adds cost, but it's useful if your layout requires it.

How Do You Plumb Grey Water Drain Lines in a Van?

Drain lines run from your sink and shower to the grey tank. They're larger diameter than fresh water lines (usually 1.5 inches) because they need to handle the faster flow and occasional blockages from food particles or soap scum.

Materials and Slope

We use plastic PVC or ABS drain pipe for grey water because it handles the temperature and chemical variation better than PEX. The pipes need a steady downward slope — at least 1/4 inch per foot. This keeps water moving and prevents buildup.

All joints are secured and the lines are routed away from fresh water pipes (no cross-contamination risk). We also install a p-trap under every drain — that U-shaped pipe that holds water and blocks smells from coming back up. Standard plumbing code applies in the van just like in a house.

Strainer and Screens

Kitchen sink strainers catch food particles and keep them out of the tank and pump lines. Without a strainer, food decays in the tank and creates odor and blockage. Shower drains also get strainers to catch hair. These are cheap to install and worth their weight in preventing headaches down the road.

How Do You Empty a Van Grey Water Tank?

The grey tank outlet is where you connect a hose to empty it. This is typically a large valve (2-3 inches) mounted on the tank or on the exterior of the van in an accessible location. You pull up to a dump station, connect your hose, open the valve, and let gravity do the work. It takes 5-10 minutes depending on tank size.

The outlet needs a clean-out port so you can access it for maintenance. If something blocks the tank (say, grease buildup), you need a way to clear it. We install a flush connection that lets you run water backward through the system to clean out buildup.

Where Can You Dump Van Grey Water?

Unlike black water, which only goes to RV dump stations, grey water can usually be disposed of several ways depending on your location:

RV Dump Stations

Most RV parks and campgrounds have dump stations designed to handle both black and grey water. You pull up, connect your grey hose to the appropriate receptacle, and empty the tank. The facility manages disposal from there. This is the most common option and it's usually free if you're staying at the campground, or $10-20 at public dump stations.

Dispersed Camping and Boondocking

In some places (national forests, public lands), it's legal to dispose of grey water on the ground away from water sources. This is called "leaving no trace" disposal — you dump the grey water 100+ feet from any stream or well, spread it out, and let the soil absorb it. Check local regulations; some areas prohibit this entirely, others are fine with it.

Private Land and Ask First

If you're camping on private land or at a private location, always ask before dumping grey water. Some landowners are fine with it, others aren't. It's worth the conversation to avoid problems.

How Do You Winterize a Van Grey Water System?

Grey water tanks are at risk in cold weather for the same reason fresh tanks are: water freezes and can crack plastic. However, grey water is slightly different — soap and dissolved minerals lower the freezing point a bit, so it's slightly more forgiving than fresh water. Still, you need a plan for winter.

Draining Before Winter

The safest approach is to drain the grey tank completely before hard freeze season. Open the outlet valve, let it empty completely, and leave the valve open so any remaining moisture evaporates. If you're not using your plumbing system in winter, this is no burden at all.

Insulation and Heat

If you need your plumbing functional in winter, wrap the grey tank and drain lines with insulation. In a heated van, this should be enough — the interior warmth keeps the tank above freezing. Some people add heat tape to critical lines for extra protection, but in a heated space it's usually not necessary.

Should You Use a Portable or Fixed Grey Water Tank?

Most van conversions have fixed tanks that are plumbed in permanently. But some people prefer portable tanks — essentially large containers that sit under the van and can be removed for dumping.

Fixed Tanks

Fixed tanks are built into the van. Plumbing connects automatically. You drive to a dump station, connect a hose, and empty it. This is convenient and clean — you never touch waste directly. Fixed tanks are what we recommend for anyone planning to van life seriously.

Portable Tanks

Portable tanks are smaller (10-30 gallons) and manual. When full, you physically remove the tank and carry it to a dump station. This is useful for short trips or if you want minimal plumbing installation. But it's labor-intensive and messy — no one enjoys carrying a tank of wastewater. Portable tanks are more of a short-term solution.

How Do You Prevent Grey Water Tank Odor?

A grey tank that gets smelly is a problem. Prevention is easier than fixing it.

Keep It Moving

Water sitting in the tank decays and smells. The best odor control is to not let water sit. Empty the tank regularly. On a week-long trip, you might empty it once or twice depending on tank size and water use. On a month-long boondocking trip, you'll empty it several times.

Enzyme and Bacterial Additives

Some people use enzyme cleaners or bacterial additives designed for RV tanks. These break down soap and organic matter, reducing odor. They work okay but aren't a substitute for regular dumping. They're useful if you'll be away from dump stations for a long time.

Tank Cleaning

Periodically (quarterly or annually depending on use), flush the tank with water to break up any buildup. We install a flush port on the tank for this reason. You connect a hose, run water through backward, and it cleans the inside. This prevents grease and soap scum from accumulating on the tank walls.

How Much Does a Van Grey Water System Cost?

Grey water system pricing scales with tank size and drain complexity:

Higher tiers include larger tanks, better access for maintenance, insulation for cold weather, and in some cases a level indicator so you know when to dump without guessing.

What Are Common Grey Water System Mistakes?

Tank Too Small

Just like fresh water, a grey tank that fills too fast is annoying. You'll be at the dump station constantly. Size it to match your fresh water capacity or larger.

Drain Line Without Slope

A horizontal drain line collects water and gets smelly. Every drain line needs slope. We make this non-negotiable in our designs.

No Strainers

Food and hair going straight into the tank creates blockage and odor. Strainers are cheap and essential.

Ignoring P-Traps

A sink without a p-trap lets sewer smell back up through the drain. Every drain needs one.

Dumping in Prohibited Areas

Check local regulations. Some places strictly prohibit grey water dumping. Getting a fine isn't worth the convenience.

How Does Grey Water System Design Fit into the Build Process?

Grey water system design is straightforward: tank size matches fresh water capacity, drain lines slope downward, and everything gets plumbed with proper vents and traps. We handle this in the plumbing design phase, which is usually step two after electrical and before finishing.

The key is sizing the tank right. Too small and you'll regret it. The extra cost of a larger tank is negligible compared to the convenience.