<font color="blue"> I can get used antifreeze for free, .25/gal on the WW fluid </font>
Beware of antifreeze. If it is ethylene glycol based, and you have a leak, the puddles can be death traps for pets and wild animals. It tastes sweet, but is deadly poison. /forums/images/graemlins/mad.gif (couldn't find a skull and crossbones)
As long as you're sure it is non-toxic, I wouldn't worry about any other stuff in it. All it does is sit in there and provide extra weight. You just want to be sure that you won't have it freeze (if applicable in your climate), cause rust, or be deadly when it comes out (as it will, most likely when you aren't expecting it if your luck is anything like most of us /forums/images/graemlins/grin.gif).