How to Build a Greywater & Urine Infiltration Pit – A Simple, Off-Grid Solution
When using a urine-diverting toilet like the Separett Tiny or Separett Villa, managing liquids responsibly is an important part of the installation. This is especially important in remote or off-grid locations where municipal sewage or a septic system is not available.
One simple low-tech solution is an infiltration pit. When properly built and placed in suitable soil, an infiltration pit allows urine and light greywater to slowly percolate into the surrounding ground.
This guide explains how to plan and build a small infiltration pit for urine and light greywater use. It is intended for small-scale installations, such as cabins, tiny homes, remote buildings, and seasonal use.
For customers who prefer a more robust, ready-made solution that requires less service than a traditional hand-dug pit, Separett also offers the Ecovault Infiltration Chamber. You can read more about that option in a separate blog post.
📍 Choosing the Right Location
Before building any infiltration system, always check local regulations. Rules for urine and greywater discharge vary depending on location. Setback requirements from wells, property lines, foundations, and surface water may also apply.
When choosing a location for a manual infiltration pit, consider the following:
Distance from water sources
The pit should be located away from wells, springs, streams, lakes, and any drinking water source. A minimum distance of 33 feet from wells or drinking water sources is commonly used as a general guideline, but local requirements may be stricter.
Distance from buildings
Keep the infiltration pit away from building foundations. The exact distance depends on local rules, soil type, and the amount of liquid being discharged.
Natural slope
If possible, place the pit downhill from the toilet and greywater source. This allows the liquid to flow by gravity and reduces the need for complicated plumbing.
Soil type
Sandy or loamy soils are best because they allow liquid to drain more easily. Avoid heavy clay soils, low-lying areas, areas with a high groundwater table, and places that are prone to flooding.
Traffic and load
Do not place the pit where vehicles may drive over it.
📏 Dimensions for a Small Household
For a typical small installation serving 1–4 people, a manual infiltration pit may be sized approximately as follows:
Width: 24–36 inches
Depth: 24–39 inches
If the system will receive more frequent use, year-round use, or greywater in addition to urine, a larger pit or multiple pits may be needed. In cold climates, the pit may also need to be deeper or placed below frost depth if used year-round.
If you expect heavier use, it is usually better to increase the infiltration capacity instead of building the system too small.
Materials You’ll Need
Coarse gravel or crushed stone
Use clean, angular drainage stone. A size range of approximately ⅝–1½ inches works well. Avoid smooth river pebbles or pea gravel, as they do not create the same stable drainage structure.
Coarse sand
Use coarse sand with a particle size of approximately 1/16–3/16 inch. The sand should be clean and free from clay, silt, or fine particles that can clog the system.
Non-perforated pipe
Use solid, non-perforated pipe to lead urine or light greywater to the pit. The pipe should be gravity-fed whenever possible.
Landscape fabric
Landscape fabric can help reduce soil intrusion into the gravel and sand layers. Use only fabric that allows water to pass through freely.
Covering material
Use a secure cover, such as treated wood, a stone slab, or another suitable lid. The cover should prevent accidental access while still allowing the system to remain protected and discreet.
Important note about illustrations
If using an illustration, make clear that the picture is not shown in exact proportions. Actual dimensions should be based on the installation site, soil type, usage level, and local requirements.
🛠️ Step-by-Step Construction
1. Dig the Pit
Excavate a circular or square hole with slightly sloped sides to reduce the risk of collapse.
For small installations, a typical pit is approximately 24–36 inches wide and 24–39 inches deep.
Make sure the bottom of the pit is level and that the surrounding soil is stable. Avoid digging in areas where groundwater is visible or where the pit may fill with surface water during rain.
2. Line the Pit with Landscape Fabric
If using landscape fabric, line the sides of the pit before adding the gravel and sand.
The purpose of the fabric is to reduce soil intrusion into the filter layers. Do not use plastic sheeting or any non-permeable material, as this will prevent liquid from infiltrating into the ground.
3. Add the Gravel Layer
Add a bottom layer of coarse gravel or crushed stone.
Recommended thickness: 12–16 inches
This gravel layer provides drainage space and helps prevent the pipe inlet from becoming clogged. Use clean, washed stone for best results.
4. Add the Sand Layer
Add a layer of coarse sand on top of the gravel.
Recommended thickness: 12–16 inches
The sand layer helps distribute the liquid and provides an additional filtering layer before the liquid reaches the surrounding soil.
Optional: A permeable fabric layer can be placed between the gravel and sand, but only if it allows water to pass freely.
5. Install the Inlet Pipe
Route a solid, non-perforated pipe from the Separett toilet’s urine outlet or from the light greywater source to the infiltration pit.
The pipe should slope continuously toward the pit so the liquid flows by gravity. Avoid low points where liquid can stand in the pipe.
The pipe should extend approximately 2–4 inches into the sand layer. Make sure the pipe end is stable and positioned so liquid can spread into the pit rather than flow directly against the side wall.
6. Backfill and Cover
After the pipe is installed, backfill the remaining space carefully.
A small amount of additional gravel can be placed around the pipe inlet to keep the area open and reduce clogging risk.
Cover the pit with a secure lid, such as treated wood, a stone slab, or another suitable cover. A top layer of mulch, straw, or soil can help the installation blend into the surroundings.
The cover should prevent accidental access and keep debris out of the system.
Using the Pit for Urine and Light Greywater
A self-built infiltration pit can be used for urine from a urine-diverting toilet.
It may also be used for light greywater, such as shower water or bathroom sink water, if local rules allow it and the system is sized properly.
Do not allow the following to enter the pit:
- Feces
- Toilet paper
- Blackwater
- Food waste
- Kitchen grease
- Harsh chemicals
- Non-biodegradable soaps
- Solids or sediment-heavy water
If shower greywater is connected, use a hair trap.
If sink greywater is connected, use a simple grease trap where appropriate.
🔧 Maintenance and Care
A self-built infiltration pit is simple, but it should still be checked regularly.
Inspect the area at least once per year. If liquid is pooling on the surface or draining slowly, the pit may be clogged, undersized, or located in soil that does not drain well enough.
Avoid harsh chemicals and non-biodegradable soaps, as they can harm soil microbes and contribute to clogging.
If urine lines are used, flush the line occasionally if mineral buildup occurs.
In cold climates, make sure the system is protected from freezing if used year-round.
A traditional gravel and sand pit may require more attention over time than a chamber-based solution, especially if the soil contains fine particles or if greywater is connected.
When to Consider the Ecovault Infiltration Chamber Instead
A self-built infiltration pit can work well in suitable conditions, but it must be built carefully. The drainage layers, soil type, pipe placement, and system size all affect how well it performs.
For customers who want a more robust and lower-maintenance alternative, Separett offers the Ecovault Infiltration Chamber.
The Ecovault Infiltration Chamber is a modular underground chamber system designed to disperse urine from urine-diverting toilets into the surrounding soil. When properly sized, it can also handle light greywater from showers and bathroom sinks.
Compared with a traditional hand-dug gravel pit, Ecovault offers a more structured installation. It provides defined chamber capacity, better internal storage volume, and a modular design that can be expanded by adding more chambers. It also reduces the amount of loose material needed and can require less service when installed correctly.
Ecovault is especially useful for:
- Tiny homes
- Cabins
- ADUs
- Remote buildings
- Off-grid bathrooms
- Installations where a more predictable infiltration solution is preferred
You can read more about the Ecovault Infiltration Chamber here.
Final Thoughts
A self-built infiltration pit can be a simple and effective way to manage urine and light greywater from an off-grid toilet installation. It uses basic materials, works without electricity, and can be suitable for small-scale seasonal use when soil conditions are right.
However, the system must be placed correctly, sized properly, and maintained over time. For customers who want a more robust solution with less service than a traditional manual pit, the Ecovault Infiltration Chamber is a practical alternative.
Whether using a traditional infiltration pit or a chamber-based system, always check local regulations before installation and make sure the solution is suitable for your soil, climate, and expected usage.