I have a skeleton spawner that flows them into the hole, but they keep landing on each other and dying. i also can't hit them in the legs; for whatever reason it doesnt register. so i have to walk up under them(the few that are there because most fell and died) and hit them and risk getting shot.
I saw a video that said you needed a 23 block drop. Not sure if I miscounted, or if they sometimes wipe each other out falling on each other or sometimes shooting each other, so I moved the floor at bottom of drop up one.
I moved 1 wall of the square(?) dungeon in a block and still to not have the water flow there quite right there (1 block is dry) to a 1x2 drop. At the bottom I have 1 wide water flowing from 1 high 4 blocks away to where I finish them off.
Y = you down 1 block
G = 1 block opening at their floor under glass block
3 = 3 high opening
D = drop chute from dungeon
1 = 1 high opening for water flow
W = water source
If you do it right, water should stop at the opening under the glass block (not on your floor).
Works best if you are standing 1 block below their floor at collection point to hit them in the legs (with anything, no need to waste a sword). Now I can get a feel for bow and arrows which I had not hardly used since 1.8 when chickens did not respawn and were often down vertical shafts on ledges. I have chicken breeding stock, but have mostly been collecting eggs from them so far.