Milking minigame
From Summertime Saga Wiki
The milking minigame is available once Diane's and Daisy's routes have advanced enough, so after the barn is built, and if your relationship with the partner is established. It can be replayed but makes the time of day pass.
Instructions
Press A and D, or tap on left and right sides of the screen. Press each side, in an alternating pattern, until the milk reachs beyond the purple lines and both machines are full. You cannot fill one side at a time and the minigame fails if one breast is milked several times in a row.
Reward
The profit ranges from $100 to $200, the gain varying according to the pregnancy status of the person milked.