Marines and Showers

We are getting in the car after leaving the commissary yesterday and Jessica says, "Mom, how long do Marines shower?" I said, "WHAT?" She said, "How long does it take for a Marine to shower?" I, thinking that she is repeating a joke to me says, "I don't know, how long?" She says, "I don't know, that's why I'm asking YOU!" (clearly exasperated with me at my lack of knowledge on the subject) So I say, "How should I know how long it takes for a Marine to shower? I guess about as long as it takes anybody else. Why do you want to know?"
She says, "The bumper sticker on that truck back there said, "Conserve water, shower with a Marine." I busted out laughing and said, "I don't know how long it takes for a Marine to shower. You'll have to ask a Marine I guess."

So, any Marines (current or former) care to answer that question for my dear, sweet almost 10 year old daughter???