Both my sis who has a septic system and my dh have said this, I do not know the reasoning behind it and my dh is not home atm. I'm pretty sure it was ammonia, because my ds would pee in the diaper once and start crying and pulling on the diaper in the crotch, his parts would be bright red and the smell was ammonia stingy like to me, and then he got small blisters on his penis from the diapers and I put him in sposies and he cleared right up. After doing the hot water wash stripping, he's back in his cloth and ok for 2 days now.
If you get a chance to ask let me know (pm me) we have been on spetic for 11 yrs. I have always used liquid (except for dipes) when i got the septic bed pumped this yr after 11 yrs... It was only half full which is amazing. I dont think its so much liquid or powder but if the det breaks down easily.