I have owned this pool for a couple years now (not original owner, there were two before me). The first time I backwashed, i ran the hose out to the back corner of my yard that butted up to a cornfield. Unfortunately I have a neighbor that lives downhill and this flooded their garden, and they came by and let me know and said that they had the same problem with the previous resident too, and the neighbor told me they had ran a "french drain" for them. It is black tubing about 1.25 inch diameter that I guess runs to the drainage system.
my problem has been that its so much narrower than the hose that it doesn't really fit and that causes a lot of headache. This year I was trying to solve this and remembered that when I first moved in I saw this partially overgrown hard plastic black grate on the ground near the pool, setting between the pool and the filter/pump. I dug the dirt and stuff that had covered it and under the grate there are two pipe openings probably 6 inches or so in diameter, and I cant really see where either goes, I still need to do some cleanup around them to get a better idea, but I wanted to ask if this was part of my pool system or if it was hopefully sewer access installed by the original pool builder?