Terumot, Chapter Eleven, Mishnah Six
This mishnah deals with a person who is cleaning out a storehouse that had been used to store terumah wheat.
If a store-chamber was cleared of terumah wheat, they do not need to force him to sit down and collect each grain, but rather he may sweep it all up in his usual manner and then deposit hullin in it.
When one cleans out a storehouse used to store terumah grains he need not make sure that each and every grain is cleaned out of the storehouse. It is sufficient to give it its usual sweeping and then he can put hullin grain in there. If there are some grains of terumah left in there, he need not be concerned about them.