You have two options for your outdoor hot tub in the winter months: drain and close it, or flush it, refill it with fresh water and keep it open. Slipping into a steaming hot tub in the winter months is wonderfully relaxing, and a great way to subvert Mother Nature's nastiest season.
Step 1 - Pre-Clean the Hot Tub
Add a degreaser such as Whirlpool Rinse to remove oils from skin and bath products. These can build up in the pipes and jets. Do this 24 hours before emptying the spa hot tub.
Carefully sink the underwater pump into the tub and activate it to remove the stale spa water.
Step 2 - Clean Vents and Filters
Extract the cartridge filter from the skimmer. Wipe around the skimmer entrance with a cloth soaked in filter cleaner. Wear gloves for this task. Soak the filter in a bucket full of water mixed with any recommended filter cleaner to dissolve oils and built-up sediment. Rinse well and set aside.
Use a good-quality cartridge cleaner to remove debris, hair, and plant bits from the filter cartridge. When the pump has emptied the hot tub, vacuum up any remaining water with the shop vacuum cleaner. Reinsert the cartridge filter into the skimmer.
Step 3 - Wipe Down and Polish all Surfaces of the Spa Hot Tub
Use a non-abrasive polish to clean all acrylic surfaces of the hot tub, especially where people sit and place their hands. Clean and polish the water taps and the control handles thoroughly.
If closing up your hot tub for winter, proceed to Step 4. If you plan to use it in the cold weather, go to Step 5.
Step 4 - Close the Hot Tub and Cover for Winter
Release all plugs and open all drains to verify the tub is completely empty of water to prevent frozen and cracked pipes. Turn off all power to the hot tub, or unplug all electrical plugs that control the spa.
Put on the hot tub cover. For winter this should be a fiberglass or wood hardtop. Slip on a protective tarp, and secure it with rope or velcro strips.
Ensure there are no air locks in the pipes. Open a pipe union near the whirlpool pump to vent out this air.
Step 5 - Refill the Hot Tub and Enjoy
Check that the filter is ready to operate, then fill the hot tub with water and test that the whirlpool jets are functioning.
Cover the hot tub with a tarp or hardcover during a snowstorm to prevent overflowing.