And this is how we solved the problem with a mineral water bottle!
It’s very simple. Firstly, make two holes – one on the bottle cap and another hole at the bottom of the bottle as shown below.
Place your thumb over the hole on the bottle cap to seal off the opening. Then, push the bottle to the bottom of the tank. When you remove your thumb, water and particles at the bottom of the tank will be sucked into the bottle. Remove the bottle with the hole at the bottom facing up and voila you have a clean tank!