I've seen several methods, but not sure ive seen one that has all these elements combined. Constructing one in this fashion ensures that every monster that spawns dies, and that all items dropped flow into one collection block. This way you can leave your character in the collection block unattended, and you will receive all drops.
The diagrams should be self-explanatory... i may make a youtube guide later on. It's basically enclosing the spawner in a 3x6 room. 3 springs go at the back of the spawner room, and create a flow that sweeps all monsters into the pit. The spawner is suspended 3 blocks above the floor, so that all monsters spawned immediately drop into the water flow. 2 springs go on either side of the collection block, as shown in the pictures following this post.
the only reason i can see that this works is if you do wait there all night. If you don't then I don't see the monsters drowning because they will bob in the water. I have not tried this myself, but with surface ones for pig drowning they almost always bob out. The only reason they drown in yours is because you wait there and they are trying to attack you instead of swim out.
Also I'm curious if there is a creeper spawn block in dungeons?
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MOD EDIT: Saying this is unnecessary and rude. If people are willing to discuss it, let them discuss it. There's a whole wide world of other topics you could explore and contribute to that you might even be interested in! How exciting!
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