What can I run through my washer to freshen it up & reduce build up?

Vinegar run through the cycle of hot water. Leave the lid open when possible on the washer to help with natural airing.

Place a cup of white vinegar on bottom rack of dishwasher. Run a full cycle using the hottest water possible.

Next sprinkle baking soda all over the racks and bottom and put some where your detergent would go. Run another full cycle using hottest water possible. That's it. That should do the trick

vinegar and bicarbonate of soda does work very well. That's all I use much cheaper than the shop bought variety.

Baking soda in with the water

do you still have your owners Manual. Mine has step by step directions for that process. Mine uses 1/4 c bleach ran in a specific sequence