It is easy to use old jars for making your mixes in, whether it is an old peanut butter jar or a jar that held spaghetti sauce. And running them through the dishwasher doesn’t get them totally clean because of how the mouths of most jars are much smaller than the inside of the jar.
Fill the jar half way with vinegar. Then add a squirt of dish soap and fill the rest of the way with hot water. Allow to sit 15 minutes then using a bottle brush, give it a quick scrub (any particles left on the jar will come right off). Rinse well with hot water. You can then put it through the dishwasher on sterilize setting to sterilize the jars.
Make sure the jars are completely dry before you put any of your Mix in a Jar recipes into it. Any moisture will cause the contents to spoil.