We recommend that you switch the vacuum bag when filled. Frequency will vary depending on how often you use the ducted vacuum system. The GX series ducted vacuums signals when comes time to change the filter-bag with it's integrated monitor system.
To access the filter you'll need to take off the dust receptacle.*
Retract, seal (with adhesive available on bag) and chuck out the used bag.
Install the new filter-bag: be sure to line up the slots on the bag with the notches on the adaptor.
Push the bag up to the retention ring. To make sure it stays fixed, rotate it 20º.
Put the ducted vacuum's dust receptacle back in place.
*To replace the bag on the GS110 model, take off the power unit's top cover rather then removing the dust receptacle.
We also recommend that after three (3) filter-bag replacements, you also change the disc-shaped filter (between motor and dust bag).
You should always use Cyclo Vac filter-bags. Failure to do so could void the warranty on your ducted vacuum.