Rubble as fill

I am going to put in another water tank,retaining wall is to be treated pine sleepers and area is about 4.5sq mtrs.

The thing is, the ground slopes and I will have about 300mm one end sloping down to 600mm the other end,I need to fill this area in and then put 100mm sand on top for tank to sit on.

I have a heap of rubble consisting of broken bricks,large and small and various sizes of broken up concrete,could I use this as fill then put some soil on top followed by the sand.

I suppose basically which would be the best way to fill this up giving me a good underneath base to allow my final 100mm of sand to be put on, I put in a tank before using sand but no fill was needed as the sand went straight onto level ground.

Thank you
Cart

i suppose the danger (if any ) in this is that your sand/soil topping may run down into the rubble leaving a sharp edge or point and once the tank is full is the time when you will find out.