After washing my Ron Hill pants, the string has separated itself from the garment. They now fall down a bit when I run. Why did it come out? How the hell do I get it back in?

The first things I do when I by a new pair of Tracksters, is cut the stirrups off and tie the ends of the drawstring together (you can still tie them when you've done this). There was a time when Tracksters came with one of those tie clasp things on the string that can be found on rucksacks and stuff. It's probably possible to buy these tie clasps at outdoor/climbing retailers to prevent accidental drawstring loss.
To get the string back in, you can attach a large safety pin to one end and simply thread it back through. It's a bit fiddly, but it works.

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GONE RUNNING

Thanks. I managed to thread it back through. I guess a wire coat hanger would also work. would probably do the job in seconds.

May take longer to get coat hanger to required shape than to thread string!?

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GONE RUNNING

Yes, but its a one off time deficit. If you keep the wire, its ready for use the next time

now that's forward thinking

Of course you're wise to the problem now and surely would take steps to prevent a re-occurance?

You'd think so

Yep, like I said: just tie the ends together!

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GONE RUNNING