Once clean the shampoo needs to be removed to make way for any whitening shampoo and then any conditioner you might want to use. While you need to do a good job of removing the shampoo and the dirt it has released, you don't have to be overly fastidious quite yet. There are two more rinsings to come so for now just get the coat ready for the next stage, whitening shampoo. If your dog has been properly brushed ahead of time and you have been careful not to cause any matting by using proper techniques to wet down the coat and massage the shampoo in you should have no problem with the shower head catching coat as you bury it into the coat to rinse out the shampoo. That will only improve with each stage of rinsing.
Old English Sheepdog, Bobtail, grooming, bathing, drying, Dog