How do I keep the sea from flooding my basement?

Question

I made my house on an island. I'm planning to build a basement, which requires the bottom of the house to be dug up. While digging, if I decide my basement is too small and forget that I built my house on an island, it could flood the basement completely. How would I be able to stop the flood and drain the remaining water quickly?

I am playing on SMP so someone else might accidentally flood my house.

Answer

If you break a block and water flows in, it cannot create water inside the basement. It only allows water to flow in, this means it will only flow 7 blocks and if you replace the block you removed it will automatically drain.

This will revert it to as it was before it was flooded except that torches and redstone are uprooted and must be picked up and replaced, and levers are destroyed. Fire is also put out and lava turned to cobblestone/obsidian.

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