I used to do that with the 1gal plastic milk cartons, put in ice cubes,
screw on the cap and give to the german shepard. The ice rattling in
there ****ed him off and he'd chew them suckers to pieces with a
vengence, then look at me all satisfied once they were annihilated.

wrote:

I throw them into my trash can when I am done - they make nice filler
to make sure I am getting my money's worth from my trash collectors.
Sorry, I could just not resist. :-)

Ocassionally, in the summer, I will wash them out, fill them with water
and freeze them. When it is frozen, I give it to my dog and he lays on
it under a shade tree to keep cool. He really seems to like it.