6" valve for sewer shutoff? Gate or ball, PVC or Cast

Sewage at my home ties into a private sewer system which has been troublesome lately and the check valve I have sometimes does not seal off 100%.

So I am looking to install a manual shut off valve in the basement of my home just before it exits out the foundation. Original 6" cast iron, plan to cut and use a mission connection.

I know a 6" cast gate valve is the standard which has been used for years but seem to carry a price tag of $600 or more. Not sure my best place to source on from and also require flange adapter to convert over to mission connection.

I have found 6" Ball valves which can be found on **** as surplus but new for under $100. They are rated to 150 PSI and are a slip connection. Easy to use mission band on.

Wondering if a 6" ball valve is OK for a sewer application. I am guessing any solids coming from my home would not cause a sealing problem for this application.

Any suggestion are appreciated for a valve that will work to meet my needs with a fair price.

quote; I am guessing any solids coming from my home would not cause a sealing problem for this application.

And why wouldn't they be? Who uses a 6" sewer for a house/residence? What you really need is a combination gate valve/backwater valve such as the J R Smith 7153. That gate valve has a "shear" gate which slices off anything that gets on the seat, which a conventional gate valve or ball valve CANNOT do. If something prevents the valve from closing it will be no more effective than your BWV.