I've seen quite a few people complain about the size of the bag on here. 12 gallon is the larger size and 9 gallon is the smaller size. Here are Filtex's dimensions (I found them to be roughly): 9 gallon, 13.5" diameter (like 12 gallon), 12" deep (more like 16"), 12 gallon, 13.6" diameter ( like 9 gallons) 24 in. depth (seems pretty close). Bags work interchangeably (well, sort of). The 12 gallon reservoir folds down at the bottom to fit a 9 gallon vacuum bottle. This is normal as the bottom will be filled with dirt and the suction will be on the sides of the bag anyway. The 9 gallon canister simply hangs inside the 12 gallon canister. This works well in most cases unless you're vacuuming up a lot of heavy stuff like garage dirt and rocks. If you do this you risk blowing the bottom of the bag and your secondary filter bag will get dirty and the engine will be filled with dirt and dust. This all works great for me in my 9 gallon Filtex vacuum. These special bags are also the cheapest option for Filtex vacuums I've found.
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