You can get a specialist solution for doing service washes I wouldnt use detergent as this can clog it up even more. I used bleach in mine though as I couldnt afford to buy the proper stuff, although you are not meant to. Soda crystals and vinegar as others have mentioned also good at disolving all the built up residues. So long as the wash is hot enough and you run it on empty. Also check your filter and pump is not blocked with hair clips, money etc. you unscrew it at the bottom of the machine and it pulls out.