All kidding aside, the prep is dehydrating and alcohol tends to dehydrate yo so.... I would wait to have the gin afterwards. Just mix it with a little Crystal light, you will do better, the lemon lime flavor, no Cherry haha! That would certainly scare the you know what out of your GI dr!Besides if you are like most by the time you get to the end of your "jug" you will be ready to hurl. The military drs make us drink 2 jugs of the stuff so I am sometimes have to pace myself or take Compazine!
Also a little tip , a few days before start weaning yourself off solid foods , only eat soup , toast , jello, for lunch and breakfast, and then the day before you have to eat your "diet". I actually can eta lightly for days before, a man couldn't. I take Topamax for seizures so it inhibits my appetite and if I don't eat I could care less. But this really helps to clean you out faster, you might find you don't have to drink all the prep. I have tablets to take as well and they do the job pretty much before the drink, so that by the time I start drinking I am almost"clean" I have actually been able to turn in my 2nd gallon jug unused, why waste it?