Me @ 5pm Friday: "Let's drain the spa, so we can refill it and get it ready for the summer. Maybe we'll even be able to soak in it tonight."
My SO: "Sounds good."
[We finally get the draining hose set up at 5:55pm]
My SO @ 6pm: "Hmm, this is going to take a while."
[check at 7pm]
[take a nap]
[check again @ 11pm ]
[check yet again @ midnight]
Finally, at 2am on Saturday morning, it finished draining.
Moral of the story: spas hold a lot more water than you think they do.