Also, presuming worst case, the perforated pipes into the field
are clogged. Would just "jetting" them be a simple, low cost fix?

(some sites say, nope, need new field - other posters on some
sites are saying "rip off", and all they did is "jet" them and
it unclogged them fine - there are no roots or such , it's a flat
field).

any thoughts ? obviously, i don't want to spend a lot of $$ on
this.


I think jetting would only be useful if the tank had failed in some manner
allowing solids to pass into the field. Fields are normally repaired by
increasing their size by adding more lines. Do you know the number and
length of the lines? Is the field heavily loaded?