The same advice could really be given for either a vacuum bag or a canister style - dump the contents into a plastic bag, seal it, and dispose of it. Even with the bags I believe our industry advice has always been to place that vacuum bag in a sealed plastic bag to prevent any fleas from escaping and to contain any eggs so they head to the dump for sure. With the canisters you also could dump the contents easily into a plastic bag and seal it for disposal. These do a pretty good job of emptying completely, but to be absolutely certain all flea eggs have been removed you could suggest that the emptied canister then be washed with a disinfectant solution. This probably is really good advice anyhow, as it helps to sanitize that canister and eliminate odors that could build up. 

On this subject, just to extend this response a bit, vacuuming is one of the most important steps the customer can (and must) do to prepare for your arrival and to do daily for a week or two after your first visit. Vacuuming the carpets can be the "stimulus" needed to get many of the fleas out of their pupa stage and to the adult stage that you then can more easily kill with your contact insecticide. Otherwise, many of the flea pupa may continue to stay in that stage for weeks longer and then appear as new adults when someone steps on them, the dog rolls on them, or any other activity contacts them. By that time your residual treatment probably is no longer effective and you will be blamed for not doing a good job. 

The diligent customer will also be directed to remove EVERYTHING from all floors - in closets, behind drapes, under and behind furniture, under the beds, etc. This exposes all of that floor surface so they can vacuum it more thoroughly as well as make those surfaces available for your treatment. It also causes the customer to remove all children's toys and shoes and other items so they can be protected from your treatment. Pulling sofas and chairs away from walls to vacuum helps them discover long lost toys, scattered popcorn, and other odds and ends that needed to be cleaned up anyhow. Even hard floor surfaces should be thoroughly vacuumed around the edges where pet hair could accumulate and provide a living place for flea larvae.

Vacuuming is NOT going to remove any substantial amount of your insecticides, particularly if you have used a liquid concentrate or aerosol. A wettable powder may be inclined to have those particles resting on the top of the carpet fibers, but liquids move down the fibers and bind to them. This is an important step, and should be done thoroughly prior to the arrival of the technician and repeatedly afterward.