How do I dewinterize plumbing in a previous foreclosed home that I am purchasing

Just slowly open the main and run aroound checking for leaks. Inspect all toilets and other fixture first for obvious signs of cracks. Was it truly winderized with antifreeze in the toilets and all lines drained? That would be rare in a foreclosure.

If the system has a well, the dewinterizing process might be more extensive.

But in escence, you have check all of the drains and use a considerable amount of water to flush the lines. All of the traps have to be filled. Water evaporates.

In a more extensive process, you may have to add bleach to the hot water heater or the lines and possibly get the lines flushed. This would be for bacteria removal. Well systems have the most problems.