I found a useful cap which has the tap built in to it and an air bleed pipe as well. You simply screw it onto the top of the 20 ltr drum and then you can pour from the drum with full control. It allows you to have drums without the danger of breaking off the tap which is normally screwed into the inlet at the bottom of the drum. I found this at my local pool/hardware shop and cost about $10
See pic attached.
See pic attached.