I hope this doesn't constitute advertising (which is not allowed), but I have successfully used the Laguna float valve in my pond. It has done an excellent job of maintaining the water level exactly where I want it and is not expensive. I cut into a water line that feeds well water to a hose bib near the pond attaching it with a small diameter flexible pvc line and a "T" connector. This eliminates the need for me to treat the water. The tricky part is positioning it so it maintains the water at the level desired. I sandwich it between the liner and a rock at the edge of my pond in an inconspicuous place. It is widely available so you should have no trouble finding one locally or online. Just Google "Laguna float valve". One word of caution, the little rubber disc that serves as the seal comes off easily, so you may want to glue it in place.

Drain and fill line ports are separate. Autofill to the sprinkler system as a source is something I can see but there are special valves to prevent back flow required in case the float valve fails. The drain is just a port that is an inch or two higher than the correct water level. That needs to be connected to a piece of pipe that is pitched down slightly to the sump. 15 feet is too far to tunnel. The drain port in the autfill tank must be plugged or water will get behind the pool wall, creating potential washouts and loss of support for the pool wall and surrounding area. A way to manually lower the pool will need to be used. That is the faucet at your cartridge filter. It works but is slow and doesn't give you the option to vacuum to waste. A 3way Jandy valve over the pump's discharge can direct water to the filter or the other port. Attaching a pipe and barbed fitting to that port allows you to connect a backwash hose, giving you a fast way to lower the pool and the vacuum to waste option you would use to get rid of an algae bloom. You don't want dead algae vacuumed into the cartridges. Its a PITA to clean them after. Scott

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.

@Aglitter, I too have seen mixed reviews on Samsung, but lately I’ve seen mixed reviews on most all brands within my budget. ;) We got one of the higher priced KitchenAids in March 2019 and around 15 months we started having issues with it maintaining temperatures. We woke several mornings to a defrosted freezer and melted ices box which resulted in all the ice water leaking to the floor via the door dispenser. I’ve since decided I don’t want an ice dispenser. Due to the hassle we’ve had with KichenAid quality & the Whirlpool customer service with our extended warranty (filed claim early July & it is still not fixed, nor have they given us our $), I’ve ruled out all Whirlpool brands. When I eliminate KitchenAid, Whirlpool, Maytag, Amana & JennAir there is not much left in my price range. I am considering Bosch, but I live in a rural area and rely mostly on big box stores to view the models. I’ve only found one Bosch and it is counter depth. I’m still looking though. We really want full size since we are a family of 5 and in a rural area. We do have a local Ferguson store, but last I checked they mostly had the high end appliances on display. I’m still trying to find some LG & GE models on display too.