It's nothing to do with the waste toner. It's most likely that the toner cartridges containing powder has not been transferred properly to paper in previous prints. The toner drum is therefore dirty with residue powder on it. Take out the toner drum which is a cylindrical greenish cartridge and use cotton buds soaked with isopropyl alcohol to clean the dirty area. Make sure everything is dry before placing back. If this doesn't work, or you again get vertical lines later after printing, you'll need to replace the whole drum which can be costly.