
Hi,
Unless you have a major disaster that requires serious work with a bucket, you should bath your Collie at least a week before a show, to allow the coat some time to return to its normal harsh texture as bathing will soften it. A bit of dampening on the day of the show, and some talc rubbed in - which must all be brushed out before they go in the ring - will normally bring the 'white bits' up nice and clean.
Before I lead you astray, you don't need to do this before every show, just when your dog is looking dirty. As 'Brainless' says, a double coated breed should not require bathing too often, as regular grooming will keep them clean.
Have just spent the day bathing my Rough Collie pup and her Mum ready for shows next weekend, not something I'd want to do every week!!
Good luck with showing, how old is your Collie and where did you get him/her?
M.