How to connect liquidtite to schedule 80 (or 40) pvc conduit?
Don't use flexible conduit for your application.
PVC is very easy to bend.  I use an electric heat gun like the kind you use for stripping paint.  The great thing about bending it is those bends remain water-tight and save you money on couplers.
If you decide to do a conduit-coupler-conduit connection you don't need a threaded connection with gaskets.  You need a PVC coupling.  You can connect them together by PVC-welding (it's like gluing), the same way PVC plumbing pipes are connected.  Notice the small amount of goo that dropped out of the connection when I welded this PVC conduit to the fitting for the box it goes into.  Check YouTube for videos on how to do this; it's really easy.  Don't get the stuff on your hands (that's why I'm wearing a latex glove in the photo) and don't inhale it.