When I used open waterers I had to clean at least weekly.
But my waterer is 'closed', no poop, no bedding, no floating organisms taking up residence and proliferating, so cleaned only 2-4 times a year....ah, the beauty of HN's.
Algae's not a problem as waterer is inside coop and rarely to never is in direct sunlight, plus, again, closed system so little to nothing gets inside to grow.
I hate those 'flip waterers', and rarely use them anymore, only to dose electrolytes in summer heat waves.......and the Vertical Nipples are a PITA too.