If they get really really gross you can just soak them in bleach for a couple of days to dissolve all the organic bits -
I know the idea of mixing bleach with something that goes in the tank freaks a lot of people out But if you rinse it out a couple of times then soak it in fresh water with a couple of drops of dechlorinator for 10mins and allow them to air dry before putting it back in the tank, you wont have any problems.
Thanks again all... I put it through a wash cycle and 2 x Rinse... it came out pretty good, so I will wait until next time to try another step, I think the vinegar will be my first try.