What is the purpose of pouring another cup of antifreeze down the drains during winterization?

Pouring antifreeze down the drains during winterization is intended to ensure that the p-traps, which are designed to hold water to prevent sewer gases from entering the home, are filled with antifreeze. This is essential during winter months when temperatures can drop below freezing. If the p-traps are not filled with antifreeze, they can dry out, allowing odors from the sewage system to escape into your living space, or even worse, freezing and causing plumbing issues.

Using antifreeze in the p-traps also helps to protect the plumbing from freezing. Given that the p-trap must maintain a liquid seal, using antifreeze ensures the traps will not freeze and crack, leading to costly repairs. Hence, the action of pouring antifreeze down the drain is a critical preventative measure to ensure proper function and safety of the plumbing system during the winter season.