Many if not most homes constructed today are hooked up to a city sewage system that filters and treats waste coming from a home's drains and toilets. However, some homes may need an alternative sewage system, usually a septic tank. This tank holds solid matter, while liquid waste is filtered and disposed of into a drain field. The solid matter is then emptied from the tank on a regular basis. When you're ready to choose an alternative sewage system, note a few important factors to first consider.