I found the link to this thread last night when I was checking in on your vase build.
I am also so glad to see that the hidden overflow works. I have wanted to try something similar, for a clean minimalist look, but have never gotten beyond sketches. I was thinking of trying it with some tubs, but now I don’t have too. I’ll definitely be following this build. I can’t wait to see the outcome. Thanks for the inspiration!
Another option for solving the problem of all the water draining out though the return in the case of power outage. Instead of a check valve, you could have the return line follow the overflow route (you could zip tie the return line to the overflow). A small tee at the top going from the return line and emptying into the overflow, perhaps airline tubing with a valve, would probably work as a siphon break for the return.
Jason