Cleaning plastic petrol tank - any tips

[slawosz]

Hi,
I have bought used fuel tank (12 lt, plastic) and there are some debris there. Do you have any tips how I could clean this?

 

[[70521]]

Soap, water and a brush.

 

[Boathook]

Soap, water and a brush.

And a rag tied on to a stick to remove any small bits left after washing.