Regarding the overflow, mine is like yours, I think. My non-pool end is below the pool end, hidden in the garden, so it doesn't trap water. I think they do them like this so that you can later modify the water level. At least that's how mine is. If it was a hole in the tile, that'd be the level you'd be stuck with. Mine is a removable/replaceable plastic pipe, that can later be shortened or replaced to make longer. Not sure why you'd want to change your level, but the option is there. And actually, it's not the overflow tube that determines your water level, it's your auto fill (if you're getting one). My auto fill sets the level of the water with a little set screw on the float. Water evaporates and is refilled, but never really gets close to the overflow tube. That comes into play only during a big rainfall. And for my setup, that's ideal. I have a solar system that fills and drains each day. If the overflow set the level, then each morning the solar system would fill, the water level would drop, the auto fill would replace the water, then at night, when the solar drains, that would overflow into the tube. That would eventually wreck havoc with your chemistry, not to mention waste water. With the auto fill level set below the overflow level, the water level can fluctuate quite a bit before it would overflow. Make sense? Same trouble you'd have if you threw a party for a "big and tall" club. How many people does it take to overflow a pool? (Water displacement.) Like I said, I didn't read your whole post, so maybe someone else covered that...
