Lots of people don't like Napisan - apparently it is the work of the devil but you decide for yourself.
These methods work well and may be more environmentally friendly....
To get rid of smells in your Nappies do this
soak them in white vinegar and cold water (500ml bottle of vinegar and top up the nappy bucket with water) overnight. Then put the whole lot in the washer, do a prerinse on cold, wash hot with a full dose of biological detergent. rinse two times with warm or cold water to shift the detergent and the nappies should smell ok.
To get rid of stains - hang them out on the washing line on a bright sunny day.
To stop your machine smelling run a service wash as and when you need to by cleaning all your filter, drawer bits etc then run a hot 90C wash with a dose of biological powder with the machine empty.
Some people find washing in biological powder helps with the stains, others use vanish etc.
For me, they are nappies, if they are a bit stained so be it - the smelly washing machine would irritate me though (which is why I do the odd service wash).
hth