My understanding is that most water pumping and sewage systems are vacuum and pressure driven and reversible -- ie there aren't closing one-way valves between y

My understanding is that most water pumping and sewage systems are vacuum and pressure driven and reversible -- ie there aren't closing one-way valves between your toilet and the sewer pipe; it's more a system where the 'pressure in' provides the 'pressure out'. Isn't it possible that this could lead to reversal or other catastrophic events -- like in the sense of sewage backing up into freshwater supplies, or massively out some exits in the system (ie some people's toilets)?