8 Essential Accessories for DIY Composting Toilets in Van Builds

Stepping into a custom-built van only to be met by a foul, lingering odor is every road-tripper’s worst nightmare. While building a DIY composting toilet is a brilliant way to save money and gain off-grid independence, success lies entirely in the details. Getting the right accessories transforms a potential biological disaster into a seamless, odor-free sanitary system that works flawlessly in a tiny space.

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Why DIY Composting Toilets Need the Right Gear

The basic science of a composting toilet is simple: keep liquids separate from solids to prevent the anaerobic breakdown that causes terrible odors. However, executing this in a moving vehicle vibrating down washboard dirt roads requires more than a plastic bucket and some sawdust. Without the correct components, you risk leaks, inadequate airflow, and pest infestations that can ruin your entire van interior.

Every component in a DIY toilet system must work in perfect harmony to manage moisture, facilitate drying, and vent smelly air outside. Cutting corners on cheap alternatives like weak fans or ill-fitting buckets leads to frequent, messy failures. Investing in specialized, durable gear ensures your toilet is as reliable and easy to maintain as a residential plumbing setup.

Urine Diverter – Separett Privy 501 Urine Separator

The urine diverter is the absolute heart of any DIY composting toilet, responsible for keeping liquid waste entirely separate from your dry solids. The Separett Privy 501 Urine Separator excels at this task because of its wide, ergonomically contoured bowl shape that naturally channels liquids forward while allowing solids to drop straight down. Molded from durable, high-density polyethylene, it is incredibly easy to clean and withstands the constant temperature swings inside a mobile van.

This diverter comes with a comfortable, insulated seat that prevents the cold-shock common with standard plastic seats in winter.

• Material: High-impact recyclable polypropylene
• Dimensions: 17.7″ L x 14.7″ W x 6.9″ D
• Included: Insulated seat, urine-separating insert, and installation template

While the installation is straightforward using the included template, you must ensure your toilet housing is deep enough to accommodate the drop of the collection funnel without pinching the drainage hose.

This separator is perfect for DIY builders who want a proven, commercial-grade interface without paying the premium price of a fully integrated retail toilet. It is not ideal for ultra-compact builds with less than 18 inches of depth available for the toilet box.

Ventilation Fan – Noctua NF-A8 FLX Premium Fan

A constant, low-draw exhaust fan is vital to pull moisture out of the solids bucket and exhaust any lingering odors to the exterior of the van. The Noctua NF-A8 FLX Premium Fan is the industry standard for off-grid toilet ventilation due to its ultra-quiet operation and legendary reliability. Drawing mere fractions of an amp, this 80mm fan can run 24/7 off your 12V house battery system without noticeably draining your power bank.

Built with self-stabilizing oil-pressure bearings, this fan resists dust and moisture buildup better than cheap computer fans.

• Size: 80mm x 80mm x 25mm
• Power Draw: 0.07 A at 12V
• Airflow: Up to 32.4 CFM (cubic feet per minute)

Because this fan uses a 3-pin computer connector, you will need to slice the wires to splice it directly into your van’s 12V DC power grid.

This fan is the ultimate choice for full-time van dwellers who value silent operation and low power consumption over all else. It is not suitable for builders who want a simple plug-and-play USB connection without doing basic electrical wiring.

Composting Medium – CocoTek Organic Coconut Coir

The composting medium acts as a moisture sponge and carbon source, quickly drying out solids and neutralizing odors. CocoTek Organic Coconut Coir is a superior alternative to sawdust because it holds up to nine times its weight in water while maintaining excellent aeration. This compressed brick expands rapidly when hydrated, providing a fluffy, odor-trapping barrier that encourages aerobic decomposition.

Coconut coir is naturally resistant to mold and bacteria, helping to keep your solids bucket hygienic.

• Form Factor: Compressed, low-sodium organic coco coir bricks
• Expansion Rate: One 1.4-lb brick yields roughly 2 gallons of loose medium
• Sustainability: 100% biodegradable and renewable resource

A common mistake is over-hydrating the block during prep; it should be damp like a wrung-out sponge, not soggy, or it will introduce too much moisture into the toilet.

This is ideal for van lifers traveling through humid climates where wood-based shavings might mold. It is less suited for those with zero storage space, as you must store spare dry bricks and a container to rehydrate them.

Liquid Holding Tank – Reliance Aqua-Tainer 4 Gallon

Storing urine safely inside a bouncing vehicle requires a robust, completely sealed container that resists leaks and odors. The Reliance Aqua-Tainer 4 Gallon is highly favored in DIY builds for its thick, rigid plastic construction and convenient square footprint that fits neatly inside standard toilet boxes. Unlike flimsy thin-walled water bottles, this heavy-duty container will not collapse under suction or crack over time.

The molded handle makes carrying and emptying the tank at public restrooms or dump stations painless.

• Capacity: 4 US Gallons (approx. 15 liters)
• Dimensions: 11.3″ L x 11″ W x 15.3″ H
• Portability: Integrated ergonomic carrying handle

To connect your urine diverter hose, you must drill a hole through the center of the threaded cap, taking care to seal the entry point with a rubber grommet to prevent odors from escaping.

This container is perfect for solo travelers or couples who want 3 to 5 days of liquid storage before needing to empty. It is not ideal for micro-builds where vertical space inside the toilet bench is limited to under 16 inches.

Solids Bucket – Hudson Exchange 5 Gallon Bucket

The solids bucket houses your compostable liner and composting medium, serving as the main repository for dry waste. The Hudson Exchange 5 Gallon Bucket is built from food-grade, high-density polyethylene (HDPE), making it incredibly sturdy and chemically resistant. Its smooth, non-porous interior is easy to sanitize, and the metal bale handle makes transport secure when it is time to empty the contents.

A five-gallon capacity provides the perfect height for comfortable seating in most custom toilet benches.

• Capacity: 5 Gallons
• Material: BPA-free, heavy-wall HDPE plastic
• Wall Thickness: 90 mil for heavy-duty durability

Make sure to measure your interior toilet box height carefully, as a standard 5-gallon bucket requires at least 15 inches of clearance, excluding the diverter and seat.

This is the industry standard choice for any DIYer building a medium-to-large toilet box. It is not suitable for ultra-low profile slide-out toilets, which require a shallower 2-gallon or 3-gallon bucket instead.

Compostable Liners – UNNI 8-Gallon Compostable Bags

Using a liner makes emptying your solids bucket a quick, mess-free task while protecting the bucket from staining and direct contact. UNNI 8-Gallon Compostable Bags are manufactured from plant-based materials and are certified compostable, meaning they break down naturally along with the waste. Their 8-gallon size offers plenty of excess material to easily tie off the bag without coming into contact with the contents.

These bags are designed to withstand moisture better than cheap biodegradable alternatives, reducing the risk of bottom blowouts.

• Thickness: 0.82 Mil heavy-duty rating
• Certifications: BPI Certified Compostable, US ASTM D6400 compliant
• Quantity: Available in packs of 50 or 100 bags

Because they are genuinely compostable, these bags will begin to degrade if left in a damp bucket for more than a week, so regular emptying is essential.

These are a must-have for van dwellers who prioritize quick, sanitary cleanups and environmental responsibility. They are not suitable for those who plan to leave waste in their bucket for weeks at a time without changing the liner.

Fan Speed Controller – Noctua NA-FC1 Controller

A fan controller allows you to adjust the airflow of your ventilation system based on humidity, temperature, and usage. The Noctua NA-FC1 Controller is a compact, precise PWM (Pulse Width Modulation) speed controller that pairs perfectly with 12V fans. It lets you dial down the fan speed for dead-silent operation at night, or crank it to full speed during hot, humid summer days to prevent condensation buildup.

This controller features a simple dial and an optional “no-stop” mode that prevents the fan from accidentally stalling at low speeds.

• Type: 3-pin and 4-pin PWM controller
• Voltage Range: 5V to 12V input
• Size: Ultra-compact 21mm x 25mm footprint

Mount this controller in an accessible spot on the outside of your toilet box so you can adjust it without opening the waste chamber.

This is an essential accessory for light sleepers and those traveling through highly variable climates. It is unnecessary for builders who prefer a simple, single-speed, always-on fan setup.

Exhaust Vent – JR Products Side Wall Vent Cover

To keep your van smelling fresh, your ventilation system must exhaust all damp air directly outside your vehicle’s metal shell. The JR Products Side Wall Vent Cover provides a clean, weather-resistant termination point for your toilet’s exhaust ducting. Molded from UV-stabilized plastic, it stands up to harsh sun and rain while preventing wind from blowing back into your ventilation line.

It features a built-in damper and a fine mesh screen that keeps insects, rain, and road debris from entering your ducting.

• Material: UV-stabilized, impact-resistant plastic
• Duct Connection: Fits standard 1-1/4″ to 2″ hoses
• Mounting: Exterior surface mount with screw holes and paintable finish

When installing this vent, apply a generous bead of high-quality butyl tape behind the flange to ensure a completely watertight seal against your van’s sheet metal.

This vent is the best choice for van builders comfortable with cutting a small hole in their vehicle’s exterior wall or floor. It is not suitable for those who prefer non-invasive venting methods, like routing ducting through a window insert.

How to Route Your Ventilation Ducting Correctly

The way you route your ventilation hose is just as important as the fan you choose. Airflow naturally resists sharp bends, so you must keep your duct run as short, straight, and smooth as possible. Avoid sagging loops in the hose, as moisture can condense in low points, pooling water and completely blocking the air path.

Whenever possible, route your ducting downward through the van floor rather than through the side wall. Venting through the floor hides the exhaust exit from sight, reduces the risk of wind backdrafts while driving, and makes waterproofing much easier. Use a rigid or wire-reinforced PVC hose that won’t kink or collapse when routing through tight cabinet spaces.

Managing Moisture and Odor in Tight Van Interiors

In a tiny van interior, moisture is the ultimate enemy that turns a composting toilet into an odor hazard. When urine mixes with feces, it creates a foul chemical reaction; keeping them isolated is only half the battle. You must actively remove ambient humidity from the toilet chamber to ensure the solids can dry out quickly and thoroughly.

To keep moisture levels low, always add a fresh layer of dry composting medium after every use to cover solids and absorb surface wetness. On humid days or during heavy rain, turn your fan speed up to draw more air through the system. Regularly checking the moisture level of your coco coir prevents it from becoming a wet paste, which stalls the drying process and invites odor.

Crucial Maintenance Routines for Off-Grid Toilets

A DIY composting toilet is not a “set-it-and-forget-it” system; it requires consistent, disciplined upkeep to remain pleasant. Wipe down the urine diverter daily using a small spray bottle filled with a mix of water and white vinegar or tea tree oil. Avoid harsh chemical cleaners, as they can degrade the compostable liner bags and damage the plastic components.

For a couple traveling full-time, expect to empty the four-gallon urine tank every two to three days and the solids bucket every one to two weeks. When emptying the solids, inspect the vent fan for dust buildup and wipe the fan blades clean to maintain optimal airflow. Always carry spare compostable liners and dry coconut coir bricks so you are never caught unprepared in remote locations.

Conclusion

Building a custom composting toilet is one of the most rewarding steps in creating a functional, self-sufficient home on wheels. By choosing high-quality components and maintaining proper ventilation, you ensure a clean, odor-free living space wherever the road takes you. Invest in the right gear from the start, stay diligent with your maintenance, and enjoy the ultimate freedom of off-grid travel.