Throughout DOD, each facility in every installation has a person assigned as the facility manager/custodian. They have a host of duties that take from 25 - 100% of their time, yet this is almost always treated as an "extra duty as assigned." It is so much more than that. At my AF installation, we have 550 persons in the Civil Engineer office, supported by 400 facility managers. Yet with all this level of support, there is not even a GS series dedicated to this duty. There may be as many as 30,000 such persons DOD-wide.
Proposal: Create a GS series just for facility managers, so they get appropriate experience credit. Also establish a method for estimating their time requirements. The Facility Manager guide at Robins AFB has an appendix with time calculations and would be a good reference.