Well, the short answer is, use a submersible pump. These “sump pumps” go right in the water and pump out water fast. The alternative is to wait hours for a gravity drain to do its job. Some hot tubs now do not even include a drain at all, just like some swimming pools have gotten rid of their floor drains. A portable, submersible pump is easily plugged in and placed in the footwall of the hot tub.
Use a thicker hose for faster pumping action, rather than a standard diameter garden hose. A 1 1/2″ utility hose can be used to drain off the water from a spa. Adapters are available for different sump pump types.
To drain the spa with a utility pump, be sure the drain hose is routed to the proper place. Place the pump in the footwall and plug it in and away the water goes. Look at the fast flow rate, the spa will be empty in as little as 10-15 minutes depending on the size of the spa. These utility pumps are also used by the pros when they break down their trade show booths at the state fair because it is the simplest way to remove hundreds of gallons of water. Or you could get a 5 gallon bucket and start bailing, but who wants to do that.
The other method is a gravity drain where a hose bib is provided by the manufacturer for a garden hose to attach to. A Gardena type connection can make the hookup easy, but the 1/2 inch or even 3/4 inch garden hose will take a long time to drain out with just relying on the force of gravity.
A variation of the gravity drain type is to actually use the suction method of getting water to drain from the spa with a garden hose. This lesser known method involves filling the spa a little so there is water in the hose, then turning the faucet off and disconnecting the water from the faucet end. Now water will start to run out of the hose backwards, thus draining the spa. This suction will continue as long as the hose in the hot tub remains under water. If the hose comes out, game over! It still takes hours for this method to drain a hot tub, so investing under a hundred dollars in a good utility pump will assure a problem free water change when it rolls around every quarter of a year or so.
Some utility pumps come with a floating ball/activator so in that case, just be sure the float is in the up position so the pump remains on and drains to the bottom. Some submersible pumps get down closer to the floor so there will be less wiping to do with the residual water.
A wet/dry vac can be the final step for a quick 1-2 empty. After the utility pump is done pumping out most of the water, a wet vac can be inserted into the footwall to get the remaining bit and also from the bucket seats.
A wipe down of the shell will assure a clean refill.
When refilling the spa from the garden hose, a prefilter can be attached to the hose to filter out impurities from the line before they get into the spa, starting off the next few months right. Clean the hot tub filter and wipe down the cover and the hot tub is ready to go.