
Assuming it is a BC you are showing. I would not bath and strip it out if him now if he has only just started, it will take his undercoat out.
Day before the show, bath the white bits and then put on a pair of rubber gloves, take a hand towel and put it in really hot water, wring and rub it into his coat, you might need to do it couple of times, then groom as normal.
If you are at LKA I am there too with a BC.