You will allways get some water left in a washer, the pump, pumps it UP a pipe, so when it switches off, that pipe full of water goes back into m/c. You will also get a build up of soap in the m/c. Do a blank wash, very hot, max temp. That will get rid of a lot of the soap in the system, and will leave clean fresh water in the m/c You will need to do it every now and again, when you 1st notice any smell. Not all the time. It seams that although most soap powders are now usable at about 40 degs. Or less, I find they do not work as well, and tend to clog more.
SD
July 2012