I have a 36" long section of 1" PVC pipe with the bell end. Few bucks at Lowes – cut to whatever length you like. I have smoothed all the edges so it doesn't scratch my spas, and so I can force the bell end into a commercial 'smooth bore' 1.25" pool hose. The 'smooth bore' hose is more expensive, but in this application, it makes all the difference in the world. The bell end is just slightly smaller than a regular coupling, but you can use the latter if you have to. It's a tight fit, so take the time to smooth the edges with a file or sandpaper, and maybe even warm the end of the hose in some hot water. Once it's assembled you can leave it that way.
I drop the pipe into the spa, and I shove a few feet of the hose into the spa behind it, letting it fill with water as I shove it in, and then I grab the whole mess and pull it out quickly, leaving only the pipe in the tub. The water starts its own siphon as soon as the hose hits the ground outside of the spa.
The pipe makes quick work of vacuuming the bottom of the tub, and the water level drops visibly. The pipe also lets it get the water out all the way to the bottom and you can move it from seat to seat to empty out bucket areas. I have to move the hose around because it comes out very fast and I don't want to flood any of my planted areas.
The pipe helps again here, because it holds the hose in place while you go attend to the open end of the hose.
About 10 -20 minutes for a 500 gallon tub. I can keep the siphon going while I run the garden hose over the tub if I want to flush it, or if I'm using "Citirbrite" or similar to clean - but if you don't have good water pressure the vac hose will drain faster than the hose can fill.
Or I just put my "pool drainer pump" on the same hose and wash cars.