Ok,Just been down and taken more pictures.
Mine work off guttering off of the roof which fills them up,inside the tank is a stocking filter on the end of the pipe,and also over the tap opening,results,clean water!The trough at the rear has not been used since last September so the water here is dirty as is still,I have diverted the water all to the front trough.
The two IBC's are connected with some washing machine pipe

so they both fill up from the rain,IBC no 2 is actually lower than the first,but for some reason it does not affect the front trough which uses the water of both.
Hope this helps?!