What is a grinder or lift pump, and do I need one?

They solve a different problem from a drainfield pump. A lift (sewage ejector) pump moves raw sewage from the house up to the septic tank when the house, or a basement bathroom, sits lower than the tank. A grinder pump does the same job but chops solids into a slurry first, so it can push through a small pressure line over a longer or steeper run. You need one only when gravity cannot carry wastewater from the house to the tank; most houses built uphill of their tank do not. Either one adds cost, power and a part that will eventually need service, which is another reason to settle house and tank elevations early.