High-rise unit servicing when the building elevator is broken.

You cannot skip the service visit. A standard high-rise unit with a 60-gallon holding tank will fill up fast with 25 workers using it for three days. OSHA 1926.51 requires one toilet for 20 or fewer workers, so you are already at the minimum. A full unit is a health violation and unusable.

Call your rental company now. They have dealt with elevator outages before. Options depend on the building and their equipment. Some companies use a portable transfer tank and a pump to move waste from the unit to the vacuum truck on the ground floor. This requires a service tech to carry equipment up the stairs and a hose run through the stairwell or a service shaft. It is labor-intensive and may need building management approval for access.

Do not try to pump it manually yourself. Portable toilet waste requires special handling and disposal at a treatment plant. The rental company is responsible for that. They might also suggest a temporary unit on the ground floor if stairs are feasible for your crew, but that does not solve the high-floor unit servicing. The key is advance notice so they can schedule a workaround.