Painting pipe is a bad idea, you end up with paint flakes everywhere.
Go natural, Bamboo comes in larger sizes also, look around, you can order it on line I suspect.
Moss etc will attach very well etc.
If you need something a bit different in shape, they sell different clays for pottery and you can heat/fire it if you have access to use/rent a kiln or some can be done at lower temps in the oven. Then you can make whatever shape you want. Porous clay is good for plants and mosses.
I guess pipe is okay for breeders etc, bare bottom tanks etc.....