Composting Toilets ‐ Design 1, The Weekender, Removing Urine.
Urine is a relatively safe item to deal with compared to the human waste we are composting. You may have heard of cases where human beings have survived by drinking their own urine - as gross as that sounds!! But too much urine or liquid in the compost heap will turn compost to "stodge" - the microbes will drown so it's really much better to remove it.
There are a number of ways to deal with urine and/or liquid. It can be-
I chose to use the French Drain option as it is quick and easy to make, cheap, and well tried and tested. Unlike the straw bale method, it is hidden. There is also no smell. French Drains have been around for hundreds of years - in the 1850's half-round clay pipes were placed in trenches with a small gap between each pipe to allow water to seep. This allowed surface water to be drained from one area and distributed over a larger underground area. They were presumably used before this time too, although it was a Mr French who gained credit for their use.
Our French Drain is a scaled-down version of this and will remove urine from the composting loo, draining it safely underground where microbes will do their thing. If water is also added, urine becomes less concentrated in salts and nitrogen etc and therefore even less of an issue. In my system, the waste water (grey water) from the small hand wash basin in the composting toilet shed, is plumbed into the same pipe and used to help dilute the urine output from the composting loo. There is a reasonably high rainfall where I am, so I guess this also helps dilute things underground.
Some more plumbing supplies will be needed. Earlier, I suggested using a 1″-1.25″ (25mm-30mm) fitting for the urine drain so you'll need to get a length of PVC pipe for the diameter you chose for the urine drain. This size is often used for plumbing waste water. You'll need relevant plumbing fittings such as "elbows".
If the shed you're placing your composting loo inside has a concrete floor, you may need to raise the bin off the floor so there is clearance for the pipe to be taken out through the back wall of the shed.
If you're lucky, the shed won't have been built and you can prepare the trench at the same time. The floor of the shed can be partially excavated to get the bin lower, if needed, so the toilet seat will end up at the correct height. The trench will go under (or through) the wall foundation at the back of the shed and continue for 3 yards, at least, to the drain.
Here are the steps-