About 20 years ago, I built a camelback like system that fit around my waist. When filled with water, it made me look really fat but helped to keep me cool and was almost hidden from view. I found that when wearing that, I could enter the clydesdale class in MTB races and no one would bat an eye. As I would race and drink, I would get lighter and lighter and by the end, I was my normal 180lb finishing the race.
I unfortunately never won this way. I had to stop and pee way too many times. But it sure was fun.
And yes, this is a joke.
But in reality, I also have an old camelback - the very first kind - that is nothing but a black sleeve that I fill and use for longer road rides (>90 miles). Works well and honestly, does not cause much of an issue.