Getting hair washed

My wife and I are at a loss as to getting our son Alex's hair washed. Currently, we wet his hair a bit, then we put on the shampoo. This shampoo is tear-free by the way. After the shampoo is firmly in his hair, we rinse it out with water in a little plastic cup. It's fine when we pour the water over the back part of his head. When the water starts pouring down the front of his head however, that's when the battle begins. He starts crying and he rubs the shampoo into his eyes, which causes them to start hurting. He doesn't want to lay down in the bath. He doesn't want to hold a cloth over his eyes. We've tried getting him to tilt his head way back, and we've also tried to get him to squeeze his eyes very tightly. My wife Jeanne has suggested to him that we could use the detachable shower hose to wash the shampoo out, and he's fine in the beginning of that, until the water hits him in the face. We don't know of anything else to try to get this boy's hair washed! We've just had to muddle through with the plastic cup of water, because that's all he'll really tolerate. If anyone reading this has any suggestions at all, feel free to leave comments with ideas. We'll try anything within reason.