Scott, thanks for your comments but I'm not sure how effective the water stop would be unless I'm missing something. Most of the water stop materials that I'm familiar with indicates that there needs to be a minimum of 2" of concrete on either side of the water stop. I don't think I'll have that thickness on the existing returns/drains. Is there a particular water stop material that you or natural one are referring to? Racket, thanks for your input too. I agree that hydraulic cements are generally expansive but I thought only during the cure period. Once cured, they should be stable. Is it safe to assume that you have had experience where the hydraulic cement did expand and you had the plaster pop? Thanks to everyone who have offered advice on this.

Thanks for info..when I look at my autofill I see two holes at the bottom..one is where the "bob" sits and one is, I'm guessing, where the water flows from the pool for the bob to sense..my actual overflow is separate. It sounds like then that the auto fill usually only acts to fill..any drainage is a result of the overflow. Correct?

If you haven't done so already, I suggest you purchase a hygrometer. Buy a good one that can be calibrated. There are YouTube videos on how to do the calibration. Does your apartment have steam radiators? Steam radiators will release a good amount of moisture into the air. Perhaps your apartment isn't as dry as you think it is. What humidity level are you trying to achieve? Randy makes a good point about using a humidifier designed to be installed inside the piano. Your goal is to keep the inside wooden components of the piano from drying out. a humidifier running inside with the lid closed should not have to filled too often especially if your apartment is not too dry.

I have an auto-fill valve in my in-ground pool. The pool is 9 years old. Recently I'm hearing a loud high pitch sound seemingly from the water source going into to auto-fill valve at the pool. I've not heard this in the previous 8+ years I've owned the pool. We've changed the float a couple of times, but to no avail. I believe the problem is the valve that the water flows thru at the water source, but can't seem to find a solution.