Spray your slow cooker with cooking spray.
Wash the red potatoes & cut into quarters & then chop those into smaller pieces- add them to your crockpot.
Peel the russet potatoes & cut the same as the red - add those to your crockpot as well.
Add the water/broth, granulated garlic, onion powder, dill, salt & pepper.
Cover & cook on high 3-5 hours or 6-8 hours on low- or until the potatoes are fork-tender.
Once soft, take a standard potato masher & start working the potatoes until you reach the consistency you desire.
Add in your butter & additional salt & pepper - mix well. Serve immediately.
*Note - you can also use an emulsion blender for this process if you like them super creamy