Once you meet the Water Dragon, head back up to Skyloft and enter Pipit’s home at night. Inside you will find his mother, Mallara. Speak with her and she will ask you to clean her house for a reward. Use the Gust Bellows to clean the entire house, from beds to windows, desks to doors. Do not stop until Mallara stops you, and by the way; the floor is not supposed to look like that.
Once the entire house is spotless Mallara will stop Link and reward him with 5 Gratitude Crystals. You can also swing by Pipit’s house at night after completing Cleaning Pipit’s House you will hear an interesting conversation between Mallara and her son.
Note: If you go back to Pipit’s house later it will be filthy again. Speak with Mallara to clean it for more Red Rupees.Skyward Sword - Side Quest: Cleaning Pipit's House,