Hi Max,
I cubic meter of concrete weighs 2.5 tonnes and that is wedged into the sides so it can never lift it. The tank has the 2x 90mm inlets and 2x 90mm outlets and one of those outlets is an overflow/vent into the tank. The tank can only fill to probably 80% where the outlet pipes come out of the tank. The issue may come when the bore pump in the tank kicks in and pumps the water half way down in the inground tank. On top of the concrete we are going to place the bricks and that is going to be another 500kg on top and then we will backfill over the top. Somebody will be cursing us one day.
