Tutorials/Zombie villager farming

This tutorial shows a safe method to separate zombie villagers from zombies as they emerge from a zombie spawner, for the purpose of converting them to villagers to start an underground village or trading hall. This is useful in situations that meet these conditions:
 * You found a dungeon with a zombie spawner in it,
 * You need a village nearby,
 * There are no villages within a reasonable distance, and
 * You have golden apples and potions of Weakness to cure zombie villagers.

An advantage to building up a village like this is that the mere act of curing zombie villagers gives you low prices for trading, especially in Bedrock Edition.

This isn't an early-game build because it requires redstone and brewing components, which are typically found in advanced play. However, it is feasible (and has been tested) in Survival mode as a late-game project.

Mechanics
While there are ways to sort items using hoppers, there is no automated way to sort mobs. It must be done manually and safely.

The idea is to use water flow to sweep the output of a zombie spawner into a hallway that contains a series of pistons that push zombie villagers into a space for conversion, and guide the other zombies to their deaths. The player (you) stands at the end of the hallway to serve as bait, safely behind a stone barrier that zombies cannot cross. The zombies and zombie villagers line up single file in the hallway. You observe the mob in the front of the line, and if it's a zombie, you flip a lever to retract a piston that lets the zombie approach you closer and fall into a mob grinder (or even a drowned farm). If the mob in front is a zombie villager, you push a button that triggers a piston to shove a zombie villager into a hole on the side.

Baby zombies are not blocked by the piston and simply fall into the mob grinder on their own.

Once you have captured a zombie villager, you can place a torch on the spawner to disable it, and then you can cure the zombie villager. Nearby the curing room you would have an underground village prepared, with a bed within 16 blocks and a workstation for the reborn villager. After the new villager claims the bed and workstation, you add another bed and another workstation, restart the spawner, and capture another zombie villager to convert.

When you have two villagers, you can continue adding beds and workstations, and breed the villagers. Or you can ensure great deals on trading by curing more zombie villagers.

Materials
This design needs:
 * 3
 * 2
 * 6(?)
 * 1
 * 1
 * 1
 * 1
 * 1 and a source of water
 * 2