Has anyone considered or tried to use Diatomaceous Earth as a septic tank treatment? Would there be any benefit to pouring DE in to your tank once a month or so? If not, what is the best natural way to keep your septic clean so you don't need to pump it.

Probably very little benefit, as it is not going to host a lot more bacteria that will munch away on the organics in the tank.

What will host more bacteria is biochar. It has LOTS of surface area and you could really boost the bacterial count in your tank if all that area was covered with actively metabolizing anaerobes. These products that you can buy at the store to flush down the toilet once a month -- essentially sawdust inoculated with bacteria -- rely on that principle, lots of surface area and some new critters to add to the mix. But that sawdust is itself eaten up in time, and the surface area goes away. Which is where biochar would have an advantage. The rate at which biochar gets eaten up by micro-organisms is in the thousands of years.

We leave a pint of milk out of the fridge a few days and or drop the insides of a rabbit that I killed a few days earlier down the pan. Seems to work OK if we have had a few days away from home but otherwise just keep flushing your waste.

quite often all the chemicals that we humans dump down our tanks (from blue water toilet stuff to detergent from washers and I've even heard of chemicals from birth control pills come through urine) damage the enzymes and bio systems that break down poo in our tanks. The more of all that that we eliminate the better the systems will run and all the better for groundwater too.

I've seen septics last for 50 years with no pumping, but those were simple systems that were not overloaded with these chemicals at old farmhouses. if you do something that will kill the bio load, you'll be pumping every couple years.