I have the original aluminum holding tank and it needs to be replaced. About 1/4th of the width is located under the galley floor; the remainder is under the pantry walls and bathroom wall framing. As it fits nearly tight between longitudinal stringers, it appears the walls mentioned will have to come out. I hope to get advice from someone who has done this (specific) replacement before; I am really hoping that there are some tips available to help make this easier. Thank you.