For connecting tubing/plumbing to a container I would try using a bulkhead fitting. You can find them at garden shops, home improvement, or pool supplies stores. They come in various sizes with slip or threaded ends. Basically you drill a hole in the wall of the container, put one side of the fitting in (it unscrews to 2 pieces) and thread the other piece onto the first. Most come with a rubber gasket to ensure a good seal.
You could even use them on liner material but it would work better if a piece of plexiglass or sturdy plastic was "sandwiched" next to the liner to prevent strain on the liner.