aus dem Nähkästchen plaudern
to reveal private/intimate details; to let others in on inside stories
Origin
The phrase comes from a time when women, sewing together, also exchanged intimate matters; the sewing box also served as a hiding place for private things. The image was popularised among others by Fontane's 'Effi Briest', where love letters are found in a sewing box.
Building blocks
Words in this expression
Examples
Beim plauderte die aus dem Nähkästchen und erzählte Dreh.
Over coffee the actress spilled some inside details and talked about the shoot.