I added the fertiliser to water when watering to gradually supply nutrients and as the time went on, rain kept topping up the barrel, leaves fell in and decomposed, mosquito and hoverfly larvae happily lived and developed in, but it was becoming apparent that the contents itself are becoming very diluted and that there is way too much solid stuff still on the bottom.
It was my aim to empty it all before winter. Firstly I used most of the liquid when watering. As I got to the thicker sludgier bottom, I tried everything. Scooping, pouring, even shovelling it out. Eveuntually I tilted the entire barrel and used the shovel to pull the sludge out into a bucket and then distributed it around the garden, hoping to enrich the soil for the years to come and maybe help the plants a bit as they are approaching the end of growing season. The barrel is now free to be used again, maybe for more fertiliser, maybe as a sore of rainwater, we shall see.