To empty the contents of an outside ashtray into the trash, unscrew the stand from the base. Different models may have different locations for the attachments, but the basic process is the same.
There should be a pin that locks the cap onto the top of the ashtray. Release it, and unscrew the stand itself from its base. Dump the contents into a trash can, taking care that there are no burning ashes. Afterwards, screw the stand back into place and lock the cap by replacing the pin. Remember to check where the specific model's pin and screw are located.