Call the rental company now and either move the service visit before the elevator goes down, or put a temporary ground-level standard portable toilet on site for that week.
On a high-rise, the vacuum truck hose and crew need elevator access to the floor where the unit sits. Fifteen floors of hose from the street is not a real option for a normal weekly pump. If the freight car is locked out for maintenance, that upstairs unit does not get pumped unless you rearrange access.
What usually works on jobs I have been on:
1. Pull the service forward into the last full day the elevator runs, then resume the week after.
2. Drop a spare unit at street level for the outage window so the crew of 40 still has a working toilet while the upstairs tank sits sealed.
3. If maintenance only blocks freight for part of a day, ask building ops for a short window the vac crew can use and put that time on the ticket.
Do not let the upstairs tank run past its normal cycle with forty people on it. A missed pump on a busy floor fills fast, and once it is past the fill line you are dealing with odor and a shut unit. Flag the outage on the service ticket so it does not look like a no-show on your contract log.
Also confirm whether the freight car has weight limits or after-hours rules the vac crew needs noted before they show up.