I have tried over the years many of the tricks with various degrees of success. Tenderizing alone by beating the poor thing has not worked for me. However, in combination with the three-dips technique, t has worked sometimes. The technique calls for dipping the octopus three times in the hot water for a second or two before putting the whole thing into the water. Timing is also a factor, and under or overbooking it results in rubbery octopus. However, now I only use baby octopi. I find it in my local supermarket defrosted. I jus put in directly on the grill, after marinating according to the recipes for only a few minutes. Some recipes call for overnight marinates, but I still only do about 10 minutes or so. Then grill it in each side for 3 minutes. For extra smokiness, I sprinkle some paprika before grilling. The trick is to serve and eat it in the next 15 minutes. When it first comes out of the grill, it is still tender. After 15 minutes, it becomes rubbery. I now don't ever bother to buy the big octopus. The baby ones are so tender that you do not need to boil them before grilling then , and then they only become rubbery if do not eat them fast enough. Do not overcook though.