Bruce, IMO what you are doing with the conical bottom makes all the sense in the world.
I currently have an aquarium with pellet trained WE in it. I wish the bottom was conical, and had a drain in it, as it would save me from siphoning debris from the bottom and hauling buckets of water to the aquarium a few times a week.
Go with your hunch, and dont let others cause you to second guess yourself!
You did not become "MR. BLUGILL" from listening to people say "That wont work"!
My only input, is if you do buy the taller tank with the screw off lid and you cut the top off of it, I would use strapping of sorts around the tank to stabilize rigidity.
Popping popcorn and watching closely!
I just re=read what Esshup said about cutting the top....THUMBS UP!
