Cleaning dishwasher - not often used - looks like rust???

[Daria B.]

Hi all- I've got a dishwasher that is seldom used. Today I had the plumber out to switch a kitchen facet. Since he had to cut off the water I wanted to make sure everything was flowing and working correctly. When I opened the dishwasher to run it to make sure it was still flowing water - I was met with surprise at the build up of "I am not sure what it is". I ran it to see if it would clean out and it didn't. What can I use besides vinegar as a solution to run through the cycle? I would post a picture but I'm using the iPhone app and there is no upload. I'll try later when I get to a real computer. Thanks!