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I have a small submersible pump from Home Depot (also see Harbor Freight), bought for my 3500 gallon above-ground pool about 15 years ago, was under $100. I have also used it in my spa (350 gallons). That blue flat hose, used for swimming pool functions like when backwashing is available in 1.5 and 2" sizes, and can go around corners.

In a stock tank or a spa? I have seen them in decorative ponds. Not sure I would count on it to save the pipes if the spa isn't running, and it's not about to heat it up to useable temps. 500w at 120v pulls 4 amps. It is less than 1/10th of a spa heater at 240v, and 1/3 of one at 120v.

Buy a Quick Drain instead. Light weight and easy to store. Can be used to drain the spa as well as a vacuum to suck up debris in the bottom of the spa in between your 3 mth water change. https://www.costco.ca/quickvac-quickdrain-spa-maintenance-system.product.10322940.html

Hot springs has ALOT. They feed jet lines from both sides off the diverter with various check valves inline to change which are working when. It's a fairly complex system. Here's one I cut out of the freeze damaged tub I am working on now. Here's another bottom left beneath the new coupling. I'd guess there are at least 9-12 in there. I can see 6 with the work I've done so far on this one. Hot springs uses the "smartjet" diverter, which typically has 6 ports and multiple positions. I would not recommend this for a hot springs. I would plug off all but 1 jet filter inlet (white standpipes) and blow through the last, using the diverter to blow out each line. HS also has "plumbing drains", small 3/8 hoses barbed off of low points to drain the pipes. Usually the left drain port. They are a great idea but unfortunately can pinch, shift, or clog and leave you with a surprise come spring. Here's one. @jimmythegreek, I would leave it running. Cheaper and safer that way. Nobody (not even me 😉) will guarantee a spa winterization. Even blowing in antifreeze. In Tahoe we would run an additional 20 amp circuit to the spa, drop a plug and space heater with thermostat set low in the equipment bay in case the main breaker trips or such. Just a thought...