Making Money with Hashish - Kenshi
Hashish is one of the most well known ways to make money in Kenshi to the point that there is an entire trading route built around Hash trade. For the most part though that trading route assumes that you will be buying Hash from towns in the Swamp rather than making it yourself. This page will have some of the same information my trading route page does but it'll also go into details about making Hash yourself and selling it.
In order to unlock Hashish Production you'll need to first unlock the Tech level required (Tech Level 3) and then research it using 1 Engineering Research. You can obtain Engineering Research from the vendor in Flats Lagoon or by exploring the world of Kenshi. To learn more about researching in Kenshi I recommend you check out my Kenshi Research Guide for more information.
Crafting Hashish can be done in a Hemp Processor and uses a character's Science skill; each craft will require 5 Hemp and 1 Water per Hash. The higher your character's Science skill the faster you'll craft Hash. Based on the math available on the Kenshi wiki it seems like the most Hash you can craft in a single day is about 33 - 35 for a total of about 42,000 Cats a day per worker.
You'll also see comments on that page talking about this being a noob trap which is partly true, the amount of Cats you make with Hash is lower than with other methods. Not only this, but you're kind of limited with where you can sell the product since it is illegal in most areas and it's not worth selling without its +400% price mark-up.
With those negatives out of the way, let's look at the positives. The primary town you can sell Hash at with a massive price mark-up is Flats Lagoon. In Flats Lagoon you can also buy 2 Engineering Research per game (more if you do the Import Game trick) which will allow you to unlock Hashish Production. If you plan your game around this then you can make a Hashish production bash close enough to Flats Lagoon to easily offload any and all Hash that you make.
For a comprehensive list of all the base locations nearby Flats Lagoon that you can grow Hashish at I recommend you check out my Kenshi Base Locations Guide. Hemp requires a Green environment to grow properly so keep that in mind when choosing an area to build. The closest areas that I would recommend are Fishman Isle and Shem. Fishman Island is 100% Green but it's a far walk and it will require a mid level team capable of surviving the onslaught of Fishmen there. Shem is easier but is only 10% Green and has less fertility which will give us significantly less yields.