Good afternoon Woldings, Does anyone have any experience with replacing black tanks in a houseboat? I am wanting to increase the capacity of the black tanks on my houseboat. i am not finding much information anywhere and not having much luck with getting what my options might be out of the marina service. Do you have to tear out the whole floor to get new tanks down in the bilge? I had heard there is such a thing as "plastic welding" where they can take the large tanks down in sections and "weld" them together. Any information would be greatly appreciated.