Actually, the issue of social degeneration of Hindu society is an extremely complex study.
Some historical recap: The mohanjodaro and harappa civilizations happened around 5000 yrs back, and historical evidence clearly indicate the people in this civilizations to be dravidians.
Even such long time back, people had an extremely developed sense of hyigene and public sanitation. The excavation yielded well developed towns with seperate areas for granary storage, public bath pools, toilets with well connected drainage outlets etc. Some archeologists even suggested that the drain outlets had sloping profile and all such outlets joined a main sewer which took the refuse out of town etc.
Somewhere down the ages, the knowledge of townplanning was lost, people started going out of villages and into the forest for morning ablusions etc. and as you have stated, from around 1000 ? AD, the practice of carrying refuse on head started.
The stratification of dravidians by aryans with their varnashram was conviniently utilized to delegate the task of sanitation to the lowest levels, later, tambrams added extra chapters and appendix on unclean castes, pollution by sight , smell , shadow and touch etc.
A pathologically disgusting degeneration.........