Say hi to John for me when you see him next. (It's Ifor by the way!)
Glycol isn't ideal to be stuffing into the environment willy nilly, it's not the most environmentally friendly stuff (it's not lethal of course.)
In real terms though, I doubt very much whether a couple of litres will make the blindest bit of difference to anything, but like most things, it's the cumulative effect that's the problem. Though if it's only a one off thing, then I really wouldn't worry about the environmental impact too much. It really isn't that bad.