The most important thing to remember when placing the bag in the vacuum is to place it so that the air current can pass through it. Typically, the bag is installed along the path between the intake tube and the exhaust port. The type of vacuum you have will determine where you place the bag along that path. If you own an upright vacuum, the bag is usually the final stop on the path: after the air is filtered, it immediately flows back to the outside. Sometimes the bag is located before the fan, as in canister vacuums, so that the air is filtered as soon as it comes into the vacuum.