How to deal with urine from a compost toilet

So you’re thinking of installing a urine-diverting compost toilet such as the Separett Villa, Tiny, Weekend or even the Privy – great! Eventually, you’ll be wondering what happens to the urine that will come out the back of these toilets… where will it go, is it safe, and is it legal to discharge it into the ground?

There are a number of options that will depend on existing services at your proposed location, ground conditions, local or national legislation and possibly other factors too.

Discharging urine to land through a soak-away pit

If you don’t have any existing sewage, grey water or black water facilities, discharging urine into a small, dedicated soak-away pit is probably the easiest option in the long term because once installed, you don’t have to worry about it – there’s nothing to clean or check if installed correctly, and it won’t smell.

The soak-away pit should ideally be dedicated to urine only and not shared with other greywater outputs like sinks and basins. The reason is that sink/basin/shower water will contain amounts of grease, fat, skin cells and other materials which can cause odours to be apparent in the pipe as they decompose – in sinks with a trap, the odour won’t get through to the building (so you won’t be aware of them) but they could be apparent through the urine pipe in the toilet (the fan will take care of most odours, but if they are very strong, even the fan won’t be able to deal with them). If you have no choice and have to share the urine soak-away with other greywater, you should consider installing an inline trap (such as a HEPVO trap) or U bend in an accessible location in the urine pipe.

Separett Soak Away

Because the discharge quantities for urine only are VERY small (usually 1.5 – 2-litres per person, per day) and spread over several visits throughout the day, the soak-away pit for urine doesn’t have to be very big.

For a ‘typical’ house with 4 occupants, a soak-away pit of around 50 x 50 x 50cm is adequate. Dig the hole, fill with hardcore and gravel etc. and run the urine pipe into the top of the pit.

Some professionals may point you towards a filter bed (aka infiltration bed), but they are really designed for greywater and not needed for the very small amount of urine a urine-diverting toilet will create. However, ground conditions or usage may dictate that you need something larger.

These are general guidelines, so adapt them to your local ground conditions accordingly – if you are concerned, you can conduct a ‘percolation’ test to measure how quickly your soil lets liquid pass through it. All soak-away pits should be in a position not generally affected by flooding, in other words, use common sense.

Urine is typically sterile as it leaves the body, but it does contain nitrogen which will act as a fertiliser in the soil. You need to ensure this doesn’t get into a watercourse or other groundwater, so in England and Wales, the Environment Agency suggest that the discharge point be at least 10 metres from a watercourse. To find out more, please visit our Building Regulations page.

Regional and national legislation might restrict or prohibit certain discharges, so do check if your area is affected. For example in Finland, it’s not permitted to directly discharge urine onto the land, however, it can be discharged if diluted with water. In such cases, products like the Ejektortank (also shown below) are ideal as they will do this automatically as you water your garden.

Because the urine is being discharged underground, there will be no odours detected above ground, and microbes and bacteria will start to colonise the area and feed off the nutrients in the urine.

Discharge to existing sink drain

Separett Discharge Mains

If you already have wastewater (aka greywater) pipework in your dwelling, it might be possible to connect the urine output from the Separett compost toilet into that pipework.

Depending on your dwelling and the layout of the pipes, this might be able to be done above the floor, or below the floor as per the following diagram.

The fan within many Separett models will remove any foul odours that might come up through the urine/greywater pipe. If you are concerned about possible odours, you should install a U bend or trap (such as a HEPVO inline trap) in an accessible position.

Discharge & dilution using the Separett Ejektortank

Separett Discharge and Dilution Diagram

The other option is to run the urine into the optional Separett Ejektortank which has a 50-litre storage capacity and can be situated outside your building. A garden hose is connected to the water input, and as the water passes through the valve on the Ejektortank, it’s automatically mixed with urine at a ratio of around 10 to 1, providing a perfect nutrient-rich feed to your lawn and other plants.

Keeping things clean and blockage free

Over time, urine can create deposits (calcification) within pipes which is why ideally, you don’t want it laying in the pipe for any time. To counter this, ensure that all pipes that carry urine have a fall of at least 1 in 10. This way, urine should flow quickly along and through the pipe.

To keep pipes blockage free, rinse the front urine bowl of your Separett compost toilet with a cup of water as often as you can remember to. Some people also find that tipping some white vinegar once a week will help. Separett also make an eco-urinal block (called a ‘Bio Drain’ block) that you can place in the front part of the toilet bowl – each time someone urinates, a small amount of enzyme will be released which will help keep the pipes free from urine deposits.

Will the urine freeze in the part of the pipe that’s outside?

Separett compost toilets are designed to be used year-round in all climates and are in use from Greenland to the Sahara Desert. Provided you have at least a 1 in 10 fall in the pipe then freezing should not be an issue. Separett recommends that in exceptionally cold climates, it would be advisable to switch to 50mm waste pipe for the parts of the pipe that are outside, but in the UK that’s probably not necessary, even if your Separett is in use all year round, but it’s your choice.

Can you just use the supplied flexible urine pipe inside and outside?

If you want to, then yes. Our only concern is that the pipe, being flexible, could ‘dip’ in places if not adequately supported and create a bend in which urine could sit for long periods of time – the consequence is a) it might freeze if the weather is below zero and b) it’s more prone to blockages from urine crystallising over time.

You might wish to consider switching to 32mm push-fit or solvent weld waste pipe – the sort that’s readily available from plumbers merchants and DIY stores. You can buy a 32mm to 32mm ‘compression’ adaptor that will go onto the fitting on the back of your Separett Villa or Weekend and then allow the connection of standard rigid pipework.

If you have any further questions, comments or feedback, we’d love to hear from you. Check out our contact page for details of how to get in touch.

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