Not sure if nipples would work. They are used to open waterer since they were chics. If I introduced that idea would be afraid they wouldn't figure it out lol
I've had all age birds either pick it right up within an hour...and others that take weeks to really figure it out.
Here's my thoughts on 'nipple training'.
First, it's good to know how much water your flock consumes 'normally', I top off water every morning and have marks on the waterers so I know about how much they drink.
-Show them how with your finger(tho that might just train them to wait for your finger), and/or manually grab them and push their head/beak onto the trigger(easier with chicks than adults).
-No other water source, best to 'train' during mild weather when dehydration is less of an immediate health risk. I do provide an open waterer late in day to make sure they don't go to roost dehydrated, especially young chicks.
It can take days or weeks to get them fully switched over, just takes observation, consistency, and patience.