I've got a 4" cast iron waste line with a slab floor. The pipe is 2 1/4" below the floor surface. The replacement flanges I have found are only 3" long. Is this 3/4" enough for a good seal? Does anyone know if there are longer replacement flanges out there? Thanks

Try the one with three allen screws in the top. Screw it to the floor also.

I've got a 4" cast iron waste line with a slab floor. The pipe is 2 1/4" below the floor surface. The replacement flanges I have found are only 3" long. Is this 3/4" enough for a good seal? Does anyone know if there are longer replacement flanges out there? Thanks
I would like to see a little more depth to work with but I can yearn, pour and caulk a lead and oakum joint in 3/4" depth. They do make a 4" deep 4" cast iron flange but you have tom search for them. Would you want me to look?
Regards, Tom

Doug, are you describing the Oatey Twist-N-Set, it has 3 screws that expand a neopreme collar.

I am describing the compression seal that has 3 allen screws on the top of the flange.