I have seen large feeders on amazon.com but you should change the water everyday. If not they could get sick from mold that grows in them. I have two feeders and I clean them every night after their last 8:30 pm feeding and refill it with new sugar water for the morning.

Gary, I don't know of one particular feeder that would serve 20+! If you have that many, you really need several feeders. My personal favorite is the Perky Pet brand, and I have several 16oz feeders with 6 ports and a smaller one with 4 ports and all have perches. Even here in our brutal deep south temps, I change my nectar every third day....I'm not filling them full at this point, but when south migration is in full swing, I add several more feeders and my hundreds of hummers will empty them out daily...and that keeps me busy each day! I would NOT leave any feeder up for one week. Good luck!