Are you trying to suck the oil out through the dipstick tube or through the lower extraction tube? On my engine, an MD2020D the lower extraction tube comes from the bottom the sump and is located below and little further forward of the dipstick tube. Also, the lower extraction tube on my engine has a rubber cap over the top of the tube which was painted green like the engine, but is easily pulled off by hand, and subsequently re-placed once the oil has been extracted (the green paint wears off in the process). I’m not familiar with your engine, but 10.5 litres of lube oil sounds an awful lot. My MD2020 is nearer to 3.5 litres or less (haven’t got the exact figure to hand at the moment).