The thought was that glycerol would draw water into the circulating compartment and hold it there (osmotic pressure) preventing cardiac drift in endurance athletes during long runs, the results were mixed. If you consume glycerol, it will stay in the blood for about 4 hrs. It is metabolized like glucose, but very slowly and doesn't raise insulin.
The thought in bodybuilding is that it would draw water from the sc compartment into circulation, thus a harder more vascular look. Too much of the stuff and it can dry out your brain and give you headaches. Mix about a 20% solution with water, if I remember it is about 5 ml/kg of a 20% solution.
My guess would be to consume it about 3 times over a 12 hr period and see what happens. That should be enough time to get the desired fluid shifts. But, you have to be lean to begin with. Too many competitors confuse fat with water retention, or perhaps I should say a state of denial with regard to what they are really holding.
W6