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You wouldn't need the submersible pump if you had a Hot Spring. They do an amazingly different thing. They put their drain on the floor. All the water drains out by itself, albeit not as quickly as a submersible. I just usually start the draining process after getting out one night. By morning, the water is gone and I'm ready to fill. No extension cords, not hassle. Oh yeah, my yard drains nicely, so the few extra hundred gallons just spreads and waters my lawn.
the drain for my CalSpa is on the floor....where else would a drain be? but I dont think the caladiums, potato ivy, perriwinkles, begonias, and soon the fall pansies would approve of that chemical water flowing into their flowerbeds!
I may be biased as a cover manufacturer, but I'm kinda surprised to not see a cover lifter mentioned.
Most manufacturers don't have a floor drain. Their drain is in the footwell on a vertical surface. Means you have to either use a sump pump or use a bucket.