Hold on fishface.
Are you rinsing laterite...or flourite? Because you don't rinse laterite...at least not the laterite we buy in the U.S. its a loose, clay like stuff, kinda beige/gray...and you layer it under your main substrate. it never rinses clean until it's gone...where as flourite, which is a rusty red color (especially if you buy flourite red) is a harded clay, more like gravel, and is indeed a HUGE pain to rinse. Just rinse it a bit, and expect some cloudiness. It'll settle out eventually, but will always kick up a little dust when you do any serious replanting/disturbing of the substrate.
I just wanna make sure you're not rinsing all your laterite down the drain, but it sounds like you have flourite red.