A dungeon grinder design I came up with for my survival world to farm skeletons. Should work just fine for zombies as well. Uses a simple water trap to push the mob into a lava blade. Under the lava are hoppers to instantly collect the drop. I tested it for a while and didn't see a single item get destroyed in the lava. You can modify the hoppers to either extend or shorten the collection point.

I was originally just gonna use my spider dungeon grinder (you can see it here) but I found that it just wasn't quick enough for skeletons. The skeletons took to long to die from the cactus and then most of the loot would fly outward right into the cactus and get destroyed. So I tried to modify the spider dungeon to make the water push the skeletons a little lower before hitting the cactus to prevent the loot from being destroyed but found that I just couldn't make it work so I decided to try and lava blade instead. I'd always wanted to make one but could get one to work well. But I found a nice simple Youtube video here on how to make one and then modified it to work in the grinder.

Additional Notes

Texture pack: Pixel Perfection