Right, just something to hold out the soil and make an easier path for excess water to get to the overflow hole.Good idea with the aggregate, that sounds easy enough So on the side of the hole and to just above its height? Think we've got the workings of a plan here !!
Yeah that sounds way too much. When you eyeball the volume with it in the bucket how much of the bucket would you say it takes up?35 x 31 x 9.5cm so from my Googling that is around 10 litre? The listing doesn't say. Edit 10 litre actually seems way too high but I've no idea how to work it out properly lol.
One way to tell is to fill it up with soil and then use a scoop of known quantity to empty it and add up the number of scoops it required.