What is pissing you off this time?

[glatt]

I'm no septic expert, but I do know that you don't want to put anything down the drain that will kill the bacteria that eat the poop. Large quantities of salt water might do that. Boiling water down the drain will probably cool down rapidly upon contact with the metal pipes to lose virtually all effectiveness before reaching any distant blockage. But if it's not spilling all over the basement floor, it probably can't hurt.

If the plan is to thaw the system out, the best bet is to insulate the ground and allow the warmth of the ground to thaw the frozen surface. Bales of hay stacked tightly together over the system probably are the best bet.

That's a big job though, and I'm not sure what it would accomplish other than making digging a bit easier. I'd leave it up to the septic contractor.

I'm glad for you that things seem to have thawed a bit.