Janet, I'm not a sewer technician (or is that a "s--- expert?"), but
based on my own experience, I think you are being way too concerned.

This house and our previous two have/had septic tanks. We never did any
maintenance of any kind on any of them, except to replace a crushed line
at the mountain house that was apparently damaged when a dump truck
backed up the driveway to unload. It was a year later when the damage
showed up when sewage backed up into the lowest drain in the house (the
basement shower drain) and flooded the bathroom floor. Needless to say,
it got our immediate attention <g>

While the guys were there, I figured I may as well have them pump out
the tank, since to my knowledge that had never been done in the 35+
years of the house's existence. Turned out to be less than half full.
Could have gone another 35 years....

In the house before that, we bought from a couple who had lived in the
house for twenty years and raised three kids (then teenagers). They had
bought it from the elderly couple who had built it and lived in it for
ten years. We lived there for eight years. The tank had never been
pumped out or had any attention at all when we sold it.

We never added anything to any of the systems and truly never gave them
a second thought. In fact, we also have/had kitchen garbage disposals in
all three houses, which to some people is considered a no-no. My wife is
a compost nut, though, so we don't put much down the drain.

The "two tanks" in your system probably means there's a 1000-gallon main
tank where everything goes at first. Then after the liquid reaches a
certain level it overflows into the second tank, and from there goes out
to the drain field and back into the ground. By that time it's liquid
fertilizer and no more. It's still only one "septic system," not two.

With only two of you in a house that was built to hold up to six (or
more?) people, you will never have a problem with it, even if you were
"big" water users, which you most definitely are not. In our case, here,
because of the combined number of bedrooms in the carriagehouse and the
big house, and because of the kind of soil we have here (hard clay), the
building codes required seven 110' drain lines. We laughingly say that
our "stuff" will never reach the end of even one of those lines, let
alone all seven.

Make sure your female visitors know not to flush tampons or sanitary
napkins, because they will take FOREVER to degrade. (This is true of
both home and municipal systems.) Toilet and facial tissue, as you know,
doesn't last long once it gets wet. Even paper towels will disintegrate
fairly quickly, but with them you could stand a chance of blocking the
line to the septic tank because of their bulk.

You're right about limiting the chemicals because they could interfere
with the bacterial stuff going on in the septic tank, but other than
that, if I were you I'd think about more fun stuff.

GB in NC

GB is pretty well correct about the septic system. However it would be
unusual to have two tanks connected together in the same system.

 As I said about having three, the one that I installed back at the
barn for the RV support facility. The other two are for the house, one
for the main part which has two bathrooms, the kitchen and laundry room.

 There is a separate system servicing a bathroom that was added on to
the end of the house. May be when they did it the distance around the
house might have been to far so they just added the tank out in the east
yard with a couple hundred feet of field line. Considering the house is
built on a slab could have a lot to do with it.

 Here the health department comes out and tests a soil sample to
determine what type system you have to put in, the standard septic or
what they call a treatment system. That could be what GB was referring
to where every thing goes into one tank and then to the other tank. That
would be a treatment system if it had two tanks.
 The test they used to run was called a perk test. But that was to low
tech for some one . All it consisted of was digging a hole with a fence
post digger and filling it up with water, if it drained out overnight
you were good. There are many different systems that qualify as a
treatment plant, you could have one.

 More than likely if you have a part of the house that was added on you
too could have two systems. There are other rules also like the number
of feet of field line required for each bath room and kitchen. If that
would be the case then rather than run the drain to the old system and
tap in to the field lines to extend them it would be a lot simpler just
to put in a new tank and what field lines that went with it.

If you want to really get in to it here might be some information.
http://www.inspect-ny.com/septbook.htm

A picture is worth a thousand words, that means there are more pictures
here.  http://www.agnr.umd.edu/users/wye/personel/Miller/septic.html

Don't know about that. I got a discount at Home Depot for opening a
charge card with them when I bought some window shades. They gave  me
$20,000 worth of instant credit!! I haven't worked since early 1996.

We did pay cash for out motorhome (insurance proceeds) and Barry's '96
Mustang convertible, but we have a loan for the Honda. We are blessed
with a financial advisor who does wonders with our money without putting
it at high risk. I'd rather pay the teeny interest that Honda wants and
let him put our cash to better use.