Mom's system was installed in 1968 and is in my best guess a 5000 gallon
stainless steel
tank. It has never been pumped. The last time I serviced it, I put an
aerorator (which essentially looks like a fishing trolling motor on a stick
that churns the sludge to aid it in
mixing the bacteria to break down faster) back into operation and added a
white powder (would appreciate someone suggesting branded names) purchased
at the local hardware store that was also supposed to aid the process of
accelerating bacteria breaking down solid waste.
My perception is that there really are only minute amounts (maybe one part
per million) of solids going into the system. What we commonly call solid
waste is really human manure, a soft-solid which actually breaks down 100%
into pure liquid water after being eaten literally by the bacteria in the
septic tank. The only solids are minute amounts of iron in the water or
similar solids. The toilet paper always seems to totally
disappear/disintegrate. My guess is it would take several hundred or
perhaps a thousand years for these metals to accumulate. In reality most of
them probably stay in solution and filter back into the back yard in what
looks like clear water.
Also, I'm told pumping actually removes the bacteria needed to break down
the waste. I can understand why one would pump if the tank is too small for
the family size or is out of bacteria balance and isn't breaking down the
waste.
My questions are this:
1) How often should a tank be pumped? I imagine it varies based on size.
How do I tell that it needs to be pumped?
2) What are the names of additives to help make the septic system run right
and how often do folks add them?
3) The trolling motor aerorator always seems to pop its local circuit
breaker in between my visits home. Is it really necessary. What percentage
of septic tanks have this feature?

Thanks in advance.