I am ready to connect my fully inspected waste system in my new home to the septic stub coming in through the wall. Before I do, I wanted to know if there is such a thing as a septic backflow preventer valve that I can install in 4" PVC. I have read that backflow valves in general, the flapper type, are not very reliable and after only a short time do not close properly or stick open. My main concern is keeping any critters out (do any get into a new, sealed septic system? I guess they technically could find their way into a leach field... tank and house...) and protection against any possible backflow or gases. I do not currently have any toilets or drains lower than the septic entry pipe, but in teh future I will have a basement bathroom and pump which I would like to protect from any backflow from the septic.

Any advice would be greatly appreciated.