i was surfing the net looking for oddities and found this, it's hillarious and great for the environment as water usage will be less over all. here is the link
http://www.fishnflush.com/about.html
a bit pricey but i think it's an awesome idea i may see if i can create one with an industrial look to put a betta or a couple crayfish in.
Why not fill it with fresh water eels? I would be cool to have the lower part a fish tank too. Ya eels or something else creepy like roaches or something.