Havent heard of buttermilk either, but to be honest, you just need something that rots quick with a high concentration of microbes for breaking down the sewage.
Dairy products are usually good, so buttermilk would work.
Onboard the vessels, we leave chunks of chicken out for a few days, then throw it into the sewage plant. We could use the chemicals and tablets we have, but bits of chicken thats gone off works REALLY well. You just want something to jump the microbe count for the sewage breakdown. Most times it isnt needed, but if any chemical goes down the toilet, it kills all the microbes. Which is why most companies tell you to put in the chemicals.. it will restart the microbes if they have been killed off. The tablets are also good because they are time delay release.. in other words it will continue to work over a few days, if chemicals are still killing off microbes...
