How to remove the smell from a dryer vent

Recently, we had an issue where an extremely wet comforter was put in our clothes dryer. We had to take the comforter out of our dryer since we heard water sloshing around in the bottom of it. Subsequently, we had a smell in the dryer, which we determined was coming from the dryer vent. We had a duct cleaning service come in and clean out the dryer vent (which was long overdue). The first time, they blew out all the lint and the second time they came, they vacuumed the dryer vent from the outside of the house to confirm that there was no residual water in the dryer vent line.

Despite this level of remediation, we continue to have a damp, mildew type smell coming from our dryer vent. When I leave the dryer connected to the dryer vent, the inside of the dryer smells, along with the vent. If I leave the dryer disconnected from the vent, the dryer is fine, but the vent still smells. So, I have confirmed that it is the vent that smells, not the dryer. I tried to run the dryer several times to 'flush out" the vent, but the smell keeps coming back.

It seems our options are to replace the dryer vent or to attempt some further type of remediation. Since our dryer vent snakes through our house and has a long run, it isn’t that easy to replace the vent. It will also likely be expensive. Our other option is to attempt to do some additional type of cleaning of the vent. However, I'm not sure what that would be. Does anyone have any ideas as to anything I can put in the vent line to remove the smell?

Any help would be appreciated.