Hmm... 36 million Republicans, 30 ml or so per day. But to control them, you'd need to do this for a few days, at the very least. Let's say a week. You'd need 0.21 l per person, so 7 560 000 litres. That would do it; they wouldn't leave the house for a few days.
Of course, you'd probably need to do this regularly to keep them off the streets.
I'd focus on legislative bodies to keep the numbers manageable. I'd also consider just bringing down their voting majorities, which might ease the logistical problems.
I'd say your biggest problems have to do with distribution rather than quantities.