many thanks for all your help i knew i would get the answer i needed. however being an impatient man i went down the longest route of removing fos wheel and inner cover, must admit i was expecting to see a large tank with easy access to pumps hahahahaha silly me should have known it wasn't that easy. only 1 bolt securing a huge slim line tank that wedges itself between the wing and the chassis, as i was already there i thought i might as'well remove the tank and clean that out also. i can only describe my findings as looking like the unkempt detergent draw of on old washing machine, full of old slimy soap etc. Cleaning the filters was easy, cleaning the inside of the tank was not, i bunged up the pump holes and then standing the tank upright refilled with very hot water with a t spoon of caustic soda just to get things going, left this for 10 minutes and then drained . Hey presto i had a tank that looked like it had come straight from the factory. cleaning the filters i used a hot tap and old toothbrush. after rebuilding and refitting the tank pumps etc i checked all was good and she was squirting like a gud un before replacing inner wing and wheel. "note" be carefull when reinserting tank into its space that you don't catch the side repeater wires as i did. kind regards Lofty