OK but that still must be awkward, even with a funnel. At least it was when I had a 5 gallon pail of hydraulic fluid to pour out. Spilled a good bit of it. They don't make a pump you can use like on 55 gallon drums?
If you look at the 5L jugs used by Liqui-Moly, the cap has two openings. The upper opening has an "easy pour" feature, much like a can of Pentosin CHF-11S, where you pull out an almost built in, clear, rubber funnel to control the flow. Petro-Canada buckets are the exact same way, the flow of oil pouring out is easy to control. You just have to ensure the smaller cap on the opposite side is also open, so the oil flows out easier.
I just put a funnel I bought from Walmart on top of the jug for good measure and pour it in, never had any problems. The first time you pour, you just have to be careful you don't tip the bucket too much, otherwise some oil might drip as you pull the bucket away. Other than that, you just need good lighting to see when it's up to level, so you know when to stop.
Personally, I don't see the need to invest in a pump for a 20 liter bucket; especially as you go through it. A pump would be understandable if this was a 208 liter drum, but when there's 15 liters or less in there, the second or third time you use it, you really don't even need the funnel on the jug.