Well, here's a way of cleaning it without too much effort but I have no idea if some of the necessary items are available at your end.

You need a small electric (preferably) concrete mixer, these are very popular here for small DIY jobs and commonly used by 2 men brick-laying teams.

You need an old car toughened windscreen (windshield) or perhaps like us the side and rear vehicle glass is toughened while the windscreen/shield is laminated.

Put the glass into a fertilizer bag or whatever for safety and smash it so it pops into those myriad of little squares, add to this a handful of smallish nuts from the come-in-handy box, Metric, UNC, UNF, Whitworth, BSF or British Cycle Thread, any will do and then put the whole lot into the tank through the filler.

Cap the tank and bungee it to the mouth of the mixer, switch on and leave for a goodly time to tumble, maybe a whole day; re-orientate 90º and do it again. Pour the rubbish out and rinse, inspect with a torch (flashlight).

Repeat if necessary.

R.