Add white vinegar, water, red vinegar, salt, pickling spice, black peppercorns, crushed red peppers, and garlic cloves to a saucepan set over high heat and bring to a boil. Once boiling, reduce to a simmer until the salt has fully dissolved, approximately ten minutes.
Remove the pickling brine from the stovetop and let cool to room temperature. You can place the hot brine in the refrigerator or freezer to cool it more rapidly.
Layer raw onion slices, hard boiled eggs, and sausages in two separate quart jars. Then pour in the cooled brine until everything is submerged. Seal the mason jars with lids and set them in the refrigerator to pickle for at least one week, then enjoy within three months.
Notes
Optional: I pierce the sausages with a fork to allow the brine to penetrate more quickly.