Alrighty, time for a small update even though it was a full evening's worth of work. I apologize in advance for the photo quality, I took these in a rush with my phone this morning on my way out the door to work:
I cut down the clear pipe like many on my other forum recommended. The outlet nozzle of the powerhead now sits about halfway down the tank's height:
And here's the tank in place in the family room behind the chairs. Again, you can see the old tank on the left:
Our backyard is FULL of large pieces of quartzite rock, so I harvested some, boiled it, and scoured it with a stiff wire brush. It's ready for the tank! Perhaps not the best choice for a river-style tank, but hey, it's free. The largest stone there will be going right next to the powerhead outlets hopefully to create some drag to pull the current downwards.
Frankie was not amused being woken up this morning with the hustle and bustle of photo taking: