How does an unstable bacterial environment lead to septic system failure?
Many household chemicals, such as antibacterial soaps and bleaches, can deplete the good bacteria sources that inhabit your septic tank. With no bacterial enzymes to digest the excess sewage, backups can and will occur.
The CRUD will settle to the bottom of the tank and will build up quicker than it is turned into a system safe effluent. When the scum and sludge layers build up, they 'pancake' the area of the clarified effluent layer eventually reducing the flowable effluent layer and allowing the system to be overwhelmed. This will allow the release of the undigested CRUD into the lines clogging them. If the CRUD does not clog the outlet line before it passes through the distribution box and drain field it will get packed into the soil and stop the drainage of the effluent into the ground. This will backup the entire septic system possibly flooding your yard and house and will require that your drain field throughout the yard be torn up and possibly replaced. (view large image)