At my former school, we didn't have a dedicated app which seems wonderful. Our method was a Google Spaces group that we uploaded all the first years to (we have not done more than 4 years so we don't know how a purge of graduates would work). Prior to that, we used Slack and prior to THAT, we used IG. The Google Spaces method is the best for us because it doesn't have a complicated sign-in and posting system. At my new institution, we have proprietary software so I can create a channel just for food rescue and it will go out to all users.
As for the logistics, we have normally indicated that the food was available up until ___ time and then after that, the custodial staff/food service providers are free to come clear the space. We haven't heard any complaints since they just adjust the time in their schedules for retrieval.
id love to connect- we're in the process of planning to introduce Share Meals as a trial with some rules attached specifically working with our university sanitarian. I do know NYU and a group of Colorado colleges have seen success using the app and am trying to also gain as much info as possible because the app can be used with an open or closed community. Would love to chat about your plan for implantation and share what challenges we're looking at if you'd like to zoom chat one day!