As a simpler alternative to pulses, you can work with a continuous flow. For this (and it works, it is my main line of defense), have water coming from the ceiling (top room) into a the central walking path of a corridor. The sides of the corridor have to be channels, so the creatures are pushed into the channels and fall in the room below.
That room (middle room) must not fill with water unless you specifically want it to, or things will stop falling into it. So you will need to dig some channels and cover them with grates, to allow the flow of water further down into the lower room, but to retain creatures.
The lower room just needs floodgates underneath the grates from the middle room so you can decide wether to drown (close the floodgates, and the water will fill all the rooms) or simply store the unfortunate creatures that got trapped. You also need to get rid of the water somehow, so the middle room keeps getting drained. It's a good idea to recycle your water and send it back to the top room. So you have a continuous flow.
In my case, the corridor (walking area) of the middle room is 3x11, with two 1x11 channels on the sides. You don't want the walking area to be 1x11, or the falling water will obstruct the path and gobos will no come. With a 3x11 corridor, the central row is where the water falls, and creatures walk on the side rows. One push, and they are in the channels.
A side effect of water pushing things (a bug?) is that most items will eventually get destroyed by the water flow. So you can get rid of the goblin's junk without breaking a sweat. First trap the gobos in the room with the grates. Then drown the gobos to "release" their equipment by closing the floodgates. Reopen the floodgates with the water flow still on, and water will start pushing the equipment around continuously, because the items are trapped in the middle room. The light items (clothing, limbs) will get destroyed/ripped apart. The heavier things (corpses, iron armor, weapons) will remain, so you can collect it later.
It gives you a nice trap that also works for waste management.