It is best to boil octopus using three full pots of water on the stove; bring all three to a boil, then drop the octopus in the first one. When the water stops boiling, transfer it to the second pot, and when that stops boiling transfer it to the third pot. When the third pot stops boiling, transfer it back to the first and let it boil for 20 minutes to finish the cooking process.
Boiling octopus can be difficult because it can overcook quickly, going from too soft to nicely tender to tough and rubbery. Before boiling the octopus it should be adequately cleaned and washed; make sure to remove the ink sack and internal organs. This is best done by making a circular cut around the beak with a knife and pulling it out. The organs should come out with it.