I never use bleach. Soda crystals in a hot wash followed by vinegar on a hot wash is supposed to be good at cleaning it out.
The soda crystals website says this:
To clean the drum, remove smells and kill bacteria add two cups of Soda Crystals to the detergent dispenser on an empty cycle and run on the longest hottest wash.
Once the cycle is complete, add 500ml of White Vinegar to the drum, and run another empty cycle on the longest hottest wash. This will eliminate any limescale and detergent from the pipes, leaving your washing machine sparkling and working more efficiently. This should be repeated every 4 - 8 weeks to ensure unpleasant odours and bacteria do not accumulate.
I've never cleaned a washing machine other than removing and cleaning the drawer, wiping the gasket and door occasionally. I do live an area with very soft water (no salt needed in dishwasher it's that soft) and I am careful not to overdose washing powder and use a very hot wash once a week for towels.
I also leave the door and drawer open when the machine isn't in use - it's in the futility room so not a problem to do that.