You take some charcoal. Burn some branches or pieces of scrap wood that's in the garage. Burn it in the little fire pit out back. Anyway, take the charcoal and smash it or grind it up until it's powdery. Use a hammer if you want. Use something.
Put it in a bucket.
Get a rotting fish. The fish market on Rainier will give you one for free, something that they can't sell or that's just going to go into the food waste. Maybe just some heads.
Add the rotting fish to the charcoal.
Let sit for a week.
Ignore the neighbors.
Do you really care if it stinks?
Puree the whole thing into a slurry.
Slop a few tablespoons of it into your watering can, fill it up with water, and there you have it.
How much money did you spend?