done more or less often.

Really? I had one pumped last year that hadn't been pumped for about 15-20
years. It was about half filled with solids and in perfect working order.
Mostly, it depends on the composition of the soil, who is using the system,
and what they allow to go into it.

Yeah, I've got about 10,000 miles on my car since the last oil/filter
change, and it's still working fine, too.