Whenever I have to wash any lambs for any reason - usually mucky bum type work (lovely job!), I use an old sheep lick bucket, with a healthy dollop of hibiscrub in warm water, and basically dunk the lamb in it, then pull it out, towel it off and let it go. Have never had any adverse reactions to this treatment - other than the lambs objecting to being dunked into a bucket of water - back end first, obviously...