Positive reinforcement. Bring up tedious and unpleasant tasks in an airy manner, talk about them like they are pleasant and nice challenge. I have a manager who says things like, "I actually really like answering questions about coupons. I feel confident about answering them and resolving their issue. I feel like I made a difference." Or if we have a lot of returns, "Hey let's make this a race and see who gets done first." Changing "mundane" to "rewarding and fun" isn't easy, but positive association helps.