draindonutsmp
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The guide

How draining actually works

A drainer is not a pump and it is not a sponge. It is a wall that walks across the surface of the water, breaking source blocks as it goes, then drops a level and walks back.

Start with the smallest one

14 blocks. Step the layer slider through it and you can see the whole mechanism in one screen.

2×2×10 · 14 blocks
  • 8Slime block
  • 2Glass
  • 2Sticky piston
  • 2Observer
Download this one[dry]YouTube tutorial →

The mechanism

Three components do all the work. Observers emit a redstone pulse when the block in front of them changes: water flowing into an empty space, or two source blocks merging into one. Pistons take that pulse and shove the assembly forward. Slime or honey glues the whole thing together so it moves as a single contraption instead of falling apart mid-sweep.

That distinction matters: an observer is not a water detector, it is a change detector. The machine is self-pacing because the ocean keeps giving it changes to react to. No clock, and nobody standing there.

Build order

  1. 01

    Wall off the volume

    The machine runs between two rails. Build the launch side and the receiving side first, because the drainer needs something to arrive at, or it flies off and desyncs.

  2. 02

    Lay the slime body

    Slime or honey binds the wall into one moving contraption. Pick one and commit: slime and honey do not stick to each other, which is exactly what makes the two-version designs work.

  3. 03

    Seat the observers

    An observer does not see water sitting there. It fires on the change, the moment water flows into the space in front of it or two sources merge. That pulse drives the pistons, which is why the machine paces itself off the ocean instead of a clock.

  4. 04

    Start it

    Most designs are held until you break a trigger block, and on the common ocean-clearing schematic that trigger is purple glazed terracotta. Glazed terracotta is used because slime does not stick to it, so it can hold the machine without being dragged along. Nothing moves until you break it.

  5. 05

    Let it cycle

    It sweeps, reaches the receiver, drops a layer, and returns along the row it just cleared, clearing going out and coming back, descending on its own until it runs out of water.

Known gotcha: the build shown in the video does not always work, while the schematic does. The author of the original ocean-clearing machine says so on the download page. If you hand-build one and it stalls, load the schematic and compare rather than assuming you misplaced a block.

Why not just use sponges?

A sponge absorbs the water around it and immediately becomes a wet sponge, which does nothing until dried. The Nether dries it instantly, but you are still in a loop of place, collect, dry, repeat. Fine for one room; hopeless at scale.

Before you run one: large contraptions and mass block updates are exactly what servers put rules around. What DonutSMP tolerates is a question for their rules and staff, not this page. Check before you build something that touches other players' land.

Block behaviour on this page is checked against the Minecraft Wiki: Observer, Slime Block and Tutorial: Flying machines. The purple glazed terracotta trigger and the video-versus-schematic caveat come from the original machine's download page.