Okay, here's my experience with it:
I burnt some wood and threw water on it and gathered charcoal and repeated until I had a bunch. I had a heck of a time grinding it up small. I tried putting it between two plywood sheets and driving over it, and that didn't work for crap, and I don't even know what else I tried. Pounding it with a big metal thing in a drywall bucket. Nothing worked well, it was very very annoying getting it small and fine enough.
Then you have to charge it with bacteria. I mean you don't have to. But if you don't then the char will suck UP nutrients and beneficial bacteria activity and you'll have a net NEGATIVE effect on soil fertility for about two years.
I mixed mine with some compost. And leaves. And then I put the mixture in either one or two five gallon buckets.
Then I had the boys pee in them until the buckets were mostly full. The boys were little so they thought it was great fun and it took them a while. (These days the boys are teenagers and it would take a much shorter amount of time!)
Then I let that sit in my garage for a few months. Maybe over the winter? IDK. By the end of it, it smelled horrendous.
This is not the right way to do it by the way. You can't use mostly straight piss. Whatever plant nutrients are in urine, it's missing some of them. You're really supposed to like, mix it up with just regular compost I think. Then pee on the compost / char pile *occasionally*. IDK. I didn't have enough compost so I did what I did.
Then I took it to the garden. Hoisting the very full buckets I realized what a disaster it would be if any of it spilled. Fortunately nothing happened. Once at the garden I scooped it out and tried to distribute it but it wanted to be clumpy. I mixed some of it up in the dirt but it was all very wet and didn't want to evenly distribute.
I came back a couple of weeks later and broke up a bunch of the chunks and worked it in a bit more with a hoe.
A year later I could notice the soil was a little better than where I hadn't done it, but IDK it wasn't very evenly applied.
10+ years later and I still come across some of the bigger chunks of char in the soil. Haven't repeated it because crushing it up was so annoying, although sometimes, sometimes, I'll take a small (about ziplock baggie) sized amount of charcoal and crumble it up and put it in the soil. With the size of my garden it's like pissing in the wind. I wish I had a better way to crush it finely.