In a mixing bowl, chopped banana peppers, green bell pepper, red bell pepper, onion, garlic, and pickling salt.
Mix the ingredients with a spoon and cover the bowl with plastic wrap.
Let sit them for 1 to 2 hours.
After 2 hours strain off all liquid.
In a stockpot, combine apple cider vinegar, white sugar, and mustard seeds and bring to a boil.
Add the pepper mixture to the pot and reduce the heat to low.
Simmer for 25 to 30 minutes.
Turn off the heat and let them cool for some time.
Place the relish into the prepared jar and cover it with the lid.
Process jar in hot water bath canner.
8 oz jar should be processed for 10 minutes and 16 oz jar should be processed for 15 minutes.
Once, the canning process is complete, the banana pepper relish must rest for 7 days to complete the pickling process.
After 7 days it will be ready to use.