Macerator pump

We have a detached garage and we are putting an apartment in the attic. We are trying to connect the plumbing in the bathroom apartment to the septic tank, which is located between the house and garage. There is not enough drop to the septic tank. We have ordered a macerator but thought that this could be installed in the garage. Now I am reading that it has to be installed behind the toilet. Is there any other option and if not, do we have to use a macerator toilet. The walls have all been covered with sheetrock and not accessible now

It sounds like you have ordered a particular macerator that is for a specific type of installation (behind the toilet). Why not just install a common sewage basin and pump system?

Any concerns about freezing in the winter?