Bit late for a reply but didnt want to appear rude. Humble apologies but I was starting work and had to get into some stuff straight away
You really are early birds today! My boy has been waking up @4:30 lately and 6 year olds have no concept of what quiet should sound like. He's a bit like a switch he is awake or asleep, with no chance of him going back to sleep for a couple of hours. Most mornings he has either watched a film or trashed his room long before I'm awake!
We (English) backfill with pea gravel and we (English) forgot to fill one with water once and it popped 1m out of the ground overnight
we located one next to a door ,the owners could not get out [the door could not open because of the lid] ,Parisians are so high maintenance...