Holding tanks never need to be full to pump them out. They can be pumped out at any time.
You shouldn't need to put any AF into the holding tank. Any little bit of effluent left will not cause a problem when it freezes. The macerator won't need any AF, either as running it dry for a few seconds will evacuate any water. Just check your lines - look for any low spots.
Not sure if you have raw water feeding the head or fresh water, but any standing water in the toilet or lines should be evacuated. If there's any low spots (or if you have a fresh water system with a pump), then address that with AF.
There's not much to it - heads are a simple system.