Выносить сор из избы (to take the litter out of the house or as we say in English to wash one's dirty linen in public) is a an expression you might have heard sometimes. The signification of this expression is similar to the English one, that is don't talk to strangers about family problems and quarrels.
Возникновение этой поговорки связано со старинными свадебными обычаями (the apparition of this expression is associated with ancient wedding customs). In ancient times, every groom would make sure that the bride was best suited for him and for the housekeeping. The purpose was to find out if she would make a good wife and housekeeper, patient, who would “умеет ли хорошо щи варить” (know how to cook a good soup), and keep the house clean.
To do so, the groom, or mostly the groom's family would come more than once in the bride's house, scattered some litter on the floor and watch how the bride would sweep the floor. And to test her patience, they would scattered more litter as soon as she has finished and say: “Мети, мети, да из избы сор не выноси, а сгребай под лавку, да клади в печь, чтобы дымом вынесло” (Sweep, sweep, yes, the litter doesn't get out of the house, and rake under the bench, and throw the dust in the oven, for the smoke to take it away.)
They would repeat this ritual of throwing litter in the oven to burn it few times. The meaning was the following: to have a clean floor at all time was important to protect the house. It was believe that bad people could harm a family if they saw litter from the doorway. And to burn the garbage was a way to scattered the troubles away like the smoke.
Выносить сор из избы (to take the litter out of the house or as we say in English to wash one’s dirty linen in public)…