Compact moss bone meal farm

A compact moss bone meal farm designed by Sebalou622 and built here by BlazedMC. The whole thing is a walled pool 13 by 11, with six pistons and six furnaces at either end. A dispenser bone meals a single moss block in the middle, the moss spreads over stone made by two lava buckets against the water, and the pistons sweep the growth off. Every fifth piston cycle the trapdoors release the water, which flushes the moss, seeds, azalea and carpet into two composters, and those turn it back into bone meal. Two droppers refill the dispenser so the loop closes and the surplus goes to two chests. It primes on 10 bone meal and then runs unattended.

You need 9 hoppers, not the 8 on screen. DreazyFN, OphieOphieNexus and EvanDaGr8 all counted the same, and the building block figure is short by roughly a stack.
The tutorial never says which way the build faces and the camera turns as it goes. Several builders tore the whole thing down to rotate it, so settle the orientation before you place anything.
Three of the four repeaters go on 4 game tick delay and one on 1 tick. guy- left the 1 tick one alone and the generator made cobblestone, which moss cannot spread onto.
If it is switched on and nothing happens, bone meal the moss block by hand once and it starts.
It stops now and then with cobblestone in the middle. toddlakin5795 clears that out and puts a moss block back over the dispenser to restart it.
On Paper 1.21.4 Oxore needed a redstone on top of the hopper above the chest, plus a completely full dispenser and top dropper, before anything reached storage.