So are you mostly supposed to use doe estrus in the drippers? Or can it be doe urine, or maybe even buck urine to anger the dominant bucks?

Timing will decide that one . During the pre-rut I'd go with a subdominant buck urine to get the local big boy fired up , then switch to estrous doe once the rut begins to kick in . Don't forget to flush out the bottle with baking soda or peroxide before you switch types . You can also use multiple drippers on the same scrape to simulate individual deer .

I've never used a dripper but always considered purchasing one. How fast do you go through buck urine and how often should you refill the dripper? My hunting area is about 45minutes to a hour away so it is a little more difficult for me to check on it frequently.

A dripper holds about 4 oz. , but you shouldn't fill it more than about halfway or it can "lock up" on you . A fill of 1-2 oz. should last at least a week , it depends on the temperature changes . Once opened urine based scents spoil after about a week anyway , synthetic scents are a better choice for longer term set ups .

I've never tried a dripper, although I've had the components to make one for some time now. I think it'd work well, especially in conjunction with another scent. During the time just before the peak of the rut, I've had good luck with esterous urine in a film canister and the tarsel glands from the previous years buck. I sealed them in a zip-loc bag and froze them. It was my idea that it would make a buck think that there was a doe in heat nearby along with another buck checking her out. So the buck you're after just can't resist checking the situation out. I always put the scents in such a way that the aproaching buck will stop, turn his head away from me and give me a great shot. A lot of times they will stop 3 8 feet away from the scent and stretch their necks out to cautiously sniff the scent. That's a good time to shoot, when they're looking away from you and standing still. The bottom line though is that the scent dripper might keep the place fresh with bucks, so when you get there, put out the tarsels or other buck scent and bring them in!