Bamboo

Cook it really really good first, since it's from the wild you don't know what is growing in it. You want to make sure to kill all germs on it before you do anything. Boil that bad boy for a long time. As for can bamboo be in tanks... Well people sell bamboo caves for pleco's so I would say yes.

Dead bamboo rots under water (I know--I tried this when I was younger).
If you can find some "clear epoxy paint" (They sell this at boat stores) then it may work.

Dead bamboo will rot, but IME no more quickly than any driftwood. Just make sure it is very well dried and boiled, and scrape off any parts that are soft or loose. Also, make sure that the entire piece is under water. A piece that is damp but exposed to air will rot much faster.

Also good to make sure it is actually bamboo. There are many plants that look like bamboo, but are not. Some of these will rot much more quickly.