I've been having some issues with my in ground Hayward pool filter (S244T). I've been noticing some sand spread throughout the bottom of the pool (20x40 in gorund). Since there was sand in the multi-port valve site glass, my local experts advised that I probably have a broken lateral. So, I changed the lateral assembly and put new sand in. Shortly after, it began doing the same thing. This time I changed the multi-port valve, lateral assembly and the sand (I've been dropping way more $$ in this than I anticipated). 

Low and behold, I am still gettting sand in the site glass (and on the bottom of the pool) after chagning everything again. The pool guys are completely stumped. 

What else could be causing sand in my site glass and pool floor after all components are brand new and was installed by the book (by me and a pool technician)