Steve wrote:

however, the solar circulation
loop apparently is filled with some sort of (clear) anti-freeze.

Bought a fresh barrel from my supplier the other day, "Solar2"
Propylene Glycol, and it's "transmission fluid red" now. But still with
the non-tox labelling.

Still tastes the same, though ;-).

I have
no idea how much there is.

Likely 5 gallons or less.

What's the easiest way to get rid of this
stuff? I'm assuming just dumping it into the ground or the sewer system
would be a Bad Thing.

Yep. Go to Home Depot, buy a bucket and lid, put it in that, label it
ANTIFREEZE, and bring it to the next hazardous waste disposal day in
your area, where folks get rid of car batteries, old paint cans, that
kind of thing.
Now, if it is REALLY proplylene glycol, it's not hazardous, but you
don't know that for a fact, so you have to assume the worst.

DJ