[mike31154]

What to cut into really depends on the individual situation. Wall sounds great unless your display happens to be situated up against an exterior wall with insulation etc. In that case, floor might be a better option despite any hassle about future repairs & colour matching floor material. You should also consider possible leaks & repairs. I would argue that through the floor the plumbing/fittings will be much more accessible & easier to fix in case of a leak.

I plan to set up a room divider tank at some point by replacing part of my kitchen counter which adjoins the dining room. I have no hesitation in tearing out the current counter, replacing it with a nice beefy stand to support a 5 foot display & drilling through the floor for a basement sump. The only wall available in my case is exterior & although I'll be opening it to replace some ancient wiring, I'll still drill through the floor under the counter for the drain & return plumbing. I've already framed a fish room directly under the intended display location to help support the main floor since the tank will run parallel to the joists.

Also must admit that I don't intend to move or sell the house. Only way I'm leaving this old house is feet first in a pine box. The kids will have to deal with selling the place, tank & all, or moving in & renovating.