Minedeas: Filter Blocks

So I came up with this idea a while ago when I couldn't get a mob grinder to work What if they add a block that only items (and maybe water) can go through this would be good for better mob grinders because the mobs would not be able to go through but the items will pass right through the block. This would also enable you to make automatic butchering machines with pistons where the animal will stand on the block and be killed then the items would fall down to under the filter where they can be easily collected. The same can be done with traps in your base they fall in a pit and get smashed by pistons and you can turn the attack from your base being raided to getting tons of loot from the attackers because the pitfal trap made from this block would not destroy items like most pitfal traps that guarantee death.

So this filter block would probably look like a sponge or this could be a use for the sponge and you would need to be able to place a pressure plate ontop of it.

I do not think there should be a recipe for this if it is a sponge instead it should be added a a rare spawn at the bottom of the ocean biome. If it would not be a sponge and it be made a new block then the crafting recipe should include hard to get items like redstone but not rare items like diamonds. I really think this would be a good use for the sponge.

Thanks for reading.