The Rebbe stressed that the pushka be actually attached to the wall of the house. The proper way to affix the pushka is similar to the way we affix a mezuza to our homes. Halacha mandates that the mezuzah be completely and firmly attached to the wall, in such a way that it is not easily removed. A mezuzah that is merely hanging on a nail or screw is not properly affixed to the house and is thus not kosher. These same rules can be applied to the pushka as well. The entire house is thus transformed into a “a Tzedakah house”.