Per IRC, are flexible PVC couplings ever allowed to be used above ground for PVC to PVC connections?
Fernco (Rubber) fittings are not approved in wall framing unless they have a metal sheathed hose clamp assembly covering the entire fitting as part of the design, Which limit them to straight couplings or reducing couplings. The reason is that vermin can chew through the rubber. They are suitable for underground but are more expensive than standard no hub couplings or regular pvc fittings. So the reason for wanting to use them for that is questionable unless there is some sort of access issue.