I just posted a new ad on Airstream Classifieds.
Used black water tank from '76 Ambassador. Has a dump valve but it might be hard to use it with new plumbing since it is glued to the current chopped plumbing. Also has the ramp form for proper drainage. In fairly good (if a bit nasty) condition. We're switching to a composting toilet so we don't need this anymore. Free to a good home.
You can contact us by filling in the form on the right hand column of the ad listing: