As always "It depends"
Common problems and solutions
1) They are not sure where to go so they come to me
2) If it's something I want to do or learn than no problem
3) See if it sets a precident and how much risk. The ODAR (other duties as required) sometimes stinks but it was in the job description. For a DBA wiring an electrical panel or UPS is not bad. Plumbing the sprinkler system is risky.
4) If its not - is there someone else?
5) I ask my boss "What do you want me to stop doing to take care of ______"
6) Remeber as president your own small business you may have to empty the presidents trash can or clean the bathroom.