I was thinking the same...wouldn't take long for a snake to destroy it, lol.
Those cement mixing tubs are black at least- not gaudy. Should be easy to disguise or support.
Only other thing I can think of- I used to have a huge plastic bathtub for bathing large dogs...it had a drain plug in the bottom too. About 40" long, about 16" deep...you
might be able to find such a thing, but like the one I had was bright turquoise... Not exactly a natural look, lol. Mine was something like this:
https://www.googleadservices.com/pag...9aACCFs&adurl=
There's also laundry sinks... (those groomer tubs get pricey pretty fast!)