[Greenbuilding] green antifreeze?

[tom]

We don't yet live full-time at the farmhouse we're rehabbing and its  
only heat is wood.  I designed the plumbing so that I can drain the  
whole supply side of the system by opening two spigots and I figured  
I'd use my compressor to blow out the drain traps until a neighbor  
suggested pouring some anti-freeze into them each time we leave.  I  
don't like the idea of anti-freeze going out into the septic tank and  
leach field- any ideas on a 'green' anti-freeze alternative?
Thanks.

ps.  Found the chainsaw discussion helpfully informative.  I've got a  
crappy Homelite I got for free some time ago, but the engine is  
giving me problems and I hate the noise and  the stink.  Looks like  
an electric may be in the future.