Caleb is fully b/f. No solids yet.
What I do is when I've got a pooey nappy, I scrape off the sludge (I've got an old knife in the laundry) and give it a bit of a rinse. Not a lot but enough to get a bit of water through it. Any bits that are stubborn and have any of the b/m fatty bits on it bet a quick going over with a nail brush. Give it a good squeeze and chuck it into the bucket.

For washing I use half a cap of Amolin and use the soak cylce. I wash with cold water mostly. Sometimes I will use a hot pre rinse if they are smelly and use dettol hygeine rinse. That isn't for stains though, just smells.

From my understanding the lux flakes can coat the fibres of the nappy and build up over time, hindering absorbtion and possibly leading to rashes.

Are you hanging them out in the full sun? I find that any stains that remain after they have been washed fade away after being hung out in the sun. Even on a cloudy day the uv rays still work.