- Place 2 liters (uncompacted) of compost in a stainless steel vessel
- Add 1 gallon of distilled water.
- Wait an hour
- Filter the solution through metal sieves until all the large particles were removed.
- Pour it through paper towels (poor man's filter paper for large quantity jobs)
A not-very-clear solution remained. It looked a lot like a cross between tea and black coffee. The humus is composted from local waste vegetable material, presumably including things like coffee grounds, tea leaves, and tree bark, all of which could give a soluble brown tincture.
I elected to try and precipitate it out using a base (assuming tannic acid and its ilk were the colorants) so I tried chalk, then sodium hydroxide. Neither changed the color significantly.
Given a dark and now contaminated sample, I tossed it down the drain.