Help with Latham, steering Please
 

Hey Guys
I have latham steering on my fountain and need to change the filter since its old and looks like axx. It has a large blue conatiner (looks like a resivoir) and then a block and a filter along with a pump on the motor. As I said I want to change the filter but then dont know what to refill with, how to refill and how to purge if necessary. I will post pics if needed but could use some help. Thanks