As others post, virtualy all septic tank systems use gravity to move the waste from the toilet to the septic tank.
Electric power is often but not allways used to move the liquid from the tank to a soakaway or leach field.
This should not matter for a few days but would be a problem in the longer term.
The solids build up in the tank until removed by a tanker truck with a suction pump, again no problem in the short term, but it would be well to consider other options for any long term disaster.

Human waste is a good fertiliser, and if treated properly wont spread disease.
In an emergency, proper treatment is unlikely to be available,therefore I would minimise the risks by only useing human waste to fertilise crops of which we eat only the above ground parts.
Fruit trees, certainly.
Potatoes, no way.

I would fit a large bucket with a toilet seat, and add earth or ashes after each use.
The contents can then be buried near trees etc, or buried deeper and crops planted above.
Neat urine is liable to kill plants, but if well diluted it may be put on the lawn without harm.
In freezing weather, simply store outside until milder weather.