Snakes can't live inside soakaway. The gas alone in your soakaway will kill them. Just incase you don't know, the gas inside your soakaway can generate electricity.
Again I ask, does the Snake live inside your poo Or they float ontop of poo?
Do you know your bathing soap water also goes into that soakaway, both the waste water from your kitchen? Do you know soaps carry chemicals that are harmful?
Again an average building has over 6 Chambers, think of it, for a snake to live inside soakaway and still find it way to a w.c, it means it must past many Chambers,so tell me. How possible is that?
Also it is completely madness living a storey building yet you are afraid that Snake will crawl out from your W.C, how?
it can never happen, thats because the 4inch pipe that carry your poo from the w.c to the soakaway has a smooth surface, Snake can not comfortable crawl on it. It not possible.
Now is it possible for Snake to crawl out from your W.C? yes it is. But that can only happen if you stay in a bungalow, ground floor and you have a breakage in the service chamber that has direct link to your w.c, I mean direct link to the toilet.
So please those of you that are busy
Flushing fuel and salt inside ur soakaway, sorry you are just wasting your money.
So hear it now, Snake can only come out from your W.C if you have a broken Chamber that is directly linked to you toilet.
Snakes don't live inside your soakaway because snakes too need oxygen.

truth i`ave been thinking about this too,its not possible for a snake to survive there, it must have crawled in from a broken part of the pipe,so instead of pouring substances, better start tracing your sewage pipe for holes