Is there a reason black tanks need to be ABS? Does waste eat through water tanks material? Is it just a thicker material in general? Just curious because its much harder to find affordable black tanks of decent size compared to fresh and grey tanks.
It's fine to use polyethylene tanks for grey and black water. Light entering a tank can fuel organic growth.. We coated our under vehicle fresh tank with Rustoleum bed-liner spray to keep the light energy out.