Les Desser wrote:
In article , Andrew
Mawson Sat, 31 Dec 2005 12:40:23
writes

In my experience caustic soda is good for fatty deposits - kitchens
etc, and sulphuric acid is good for hair balls - baths & showers.
Beware that sulphuric acid will stain baths and shower trays so be
very careful how you pour it.


Quote from http://proterraonline.homestead.com/homecare_drains.html

Although it is sold commercially as a drain cleaner, never use caustic
soda to open a drain. It will combine with the grease from soap or food
wastes to form an insoluble compound.

The soap it forms will always be water soluble, but not always
instantly. A bar of soap would be pretty useless if it dissolved as
quickly as you want a blockage to disappear. Also, the soaps of fatty
acids are often much bulkier than the original oil/fat.