Oh no, this was the cold water tank, 100% sure on that, considering it emptied when I drained the cold water the first time to help clean the **** (oh come on, word filtering the first four letters of Sir Thomas Crapper, on the plumbing forum too. Heresy!) outta the bottom. It emptied, cold water went off. Heating tank (more of a big square bucket really) remained full and even filthier.