The nearest we could figure was this...
When the area where the water was leaking OUT of the pipe formed a "pocket" and the area itself became so saturated with water that it wasn't even draining away, it "swirled" around and found itself being "pulled back into the pipe" (if you will) and then deposited on the floor of the pool.
As I mentioned before, it wasn't a lot of sand, just enough to say, "HUMMMM?"
As the for sand from the skimmer end - that stuff was ending up in the "secondary" strainer basket (right after the pipe came up through the concrete and before the the "diverter valve" on the filter/pump. We knew we had some sort of problem, but not the size or extent until I ended up digging it all out.
Now, as for where the sand itself came from...our pool was an "inground" unit - when they dug out the clay/dirt, they built the sides (metal) then they poured in tons of fine sand, smoothed it out like concrete (to make up the pool's floor) then they installed the liner, as they did, they added water and smoothed out any imperfections in the sand and the liner as it filled (the deep end was 7.5' and it sloaped up to the shallow end of 3.5'). When the water level reached the "bottom of the shallow end" it was then that the crew started to back-fill around the outer edge of the metal-shell with the same type of sand. That's the area where the crew made all the connections into and out of the pool with the piping and skimmer stuff.
When the sand was going in as back-fill, it was "watered down" to help compact and compress it. Then the water in the pool was brought up to the same level. It took about 5 hours for the process to be completed.
So, around all the pool's outer shell was a layer of sand (or buffer if you will) and that was the area where all the broken piping was laying. I/P & O/P.
Like I said, it was an area just large enough for a skinny-assed 12yo to spend his summer in.
