bottle brush works well in the drawer slot, gets into all the nooks. if there is a dishwasher put the drawer itself in there. for the mashine itself, clean the seal first with hot soapy water, then bleach then wash off well with clean water. clean out the filter. run a hot hot hot service wash with nothing in.
hope it ok after that. nothing worse than a dirty washer with someoe elses grime...
the drawer, and the slot where it goes, probably have black mildew growing on the residue of soap and softener. You can spray it using Kitchen Cleaner with Bleach, the bleach will kill the midew so it cleand off easier, and, scrubbed with a nylon or tooth brush, the residue will clean off. Use the same cleaner on the rubber door seal, especially its grooves.
You can take out the soap drawer and scrub it in hot water.
the soapy residue in the drum will come away with 90C hot washes with a cup of washing soda (no soap or clothes for this). If the water goes grey and foams up, that's the old soap sludge dissolving, do it again until it stays clean.
Take out the pump filter (some water will dribble out) and remove the cotton, bra-wires and loose change.
Washing soda is quite cheap and very good for cleaning off grease and soap scum.
A friend has just moved into a rented flat which has integrated appliances. The (oldish) washing machine has clearly never been cleaned and when you take the (disgusting) drawer out, it's thick with slime, old softener and black gunk. It's actually quite solid. Any suggestions of how to clean? The drawer can be soaked in bleach but I'm not sure whether that might be too drastic for the rest of it and there's no point in trying to run anything to clean the drum till the gunk is cleared. You wouldn't want to put your clothes in it, that's for sure.