I have found that for our water, lime juice is more effective than Tang, lemon juice, or vinegar.
We just got a water softener, so I only use the lime juice every few loads now, but previously I added a bit to each load during the "light wash" phase, and it prevented buildup on the machine (and on the dishes--- our glasses slowly turned opaque if I stopped using it!

)
To remove the initial buildup, I just used a lot of lime juice in a few loads of dishes in a row.
alsoSarah