Slight hijack, I’m afraid I don’t have much to offer in regard to an answer to the OP, but…
Shampoo as a lube?! Didn’t that sting like crazy? I was under the impression that any kind of soap is strictly for exterior use? Most girls I’ve witnessed showering never use soap on the (ahem) inside, but what you describe would certainly get the shampoo distributed way beyond any part of the body that ever sees the light of day.
Am I completely misinformed?