How do i get maintenance workers to pick up the trash in zoo tycoon?

you click on the worker, then click on the little arrow icon in his box. there will be a list of 4 duties. you can assign them to do any or all of the tasks. you can also assign zoo keepers to exhibits. click on the zoo keeper, click the same arrow icon, then run your arrow over the exhibit you would like to assign. if the squares are green you can assign a zoo keeper, if it is red you must assign a scientist. if it is a tank you must assign a marine specialist.