A better substitute for a funnel than a rolled-up, taped piece of cardboard is an empty food tin a 1lb/450g one will do - with a hole punched near the joint between the bottom and the side. (Don't punch the hole in the centre of the tin as you'll have less control over the flow. ) Hold the tin at an angle while you pour through it.
Or, cut the bottom off a plastic soft drinks bottle and turn it upside-down.