Forgive me asking this "odious" question in this group, but I know that
a lot of keen gardeners live on isolated properties which are not
connected to the usual sewage system.

We have a reasonably-sized septic tank embedded in the front garden and
we understand that the previous owner had it cleaned every year, at a
cost of about £120. There has been a suggestion that this annual
cleaning is a bit excessive. On the other hand, I have read that if the
solids mount up and leave the tank and move into the soakaway area then
the soakaway area becomes clogged and you then have to build a new
septic tank at another (clean) spot - which is a real bother and a
considerable expense. So, clearly, regular cleaning is worthwhile.

But how often is regular for a two-person household?

Any ideas?

Thanks,
Eddy.