Thank you very much for the answers!! I was about to lower the hot water tank as MDQ Heating said, but try something else before it worked: I heated the plastic nipple with a lighter, and began to thread it on the thermo outlet, without Teflon or anything, trying to keep it More right possible. After he got in quite a bit, I took it out (it was left with the thread half blurred on one side, I guess copying the mess inside) and I put hemp and seals it. I put it back very slowly and SURPRISE, grabbed! He had tried before with several nipples but without the step of heating it, and he always lost. Now he has been walking for a day, without losing a drop. The bad news is that now I discovered a puncture in the base, and there I think I ran out of adventure to try to save the thermos :(. Anyway, thank you very much for the answers !!!