How to Drain and Refill a Hot Tub

Draining is the one job where the water leaving matters as much as the water arriving. A few hundred gallons has to go somewhere, and where it goes depends on what is in it and on what that water will do to the ground around your tub once it gets there.

Three things decide whether this goes well: the firebox is cold, the sanitizer is neutralized, and the water is led properly away.

Not sure where your water is? Check your readings.

Before you pull the plug

Let the firebox go completely cold

On a wood fired or hybrid tub, never drain below the fill line while the firebox is hot or even warm. The firebox is cooled by the water around it, and dropping the level while it still holds heat is what warps it.

Let the fire burn out and give it hours rather than minutes. If in doubt, wait longer. This applies whether you are draining for a clean, a water change or the winter, and it is the single instruction on this page that protects the tub itself.

Neutralize the sanitizer

Test first, because the reading decides where the water can legally and safely go.

Let it fall to zero if you can plan ahead. Stop dosing, leave the cover off for a day or two, and it dissipates on its own. If you cannot wait, a neutralizing agent does the same in minutes. Either way, retest after fifteen minutes to confirm zero before the water goes anywhere near plants, soil or a waterway.

Let the water cool

Very hot water damages roots and soil life, and in cold weather it does something else: it melts snow and then refreezes as a sheet. Let it come down before it goes out.

Lead the water away from the tub

This is the part most people get wrong, and it causes more trouble than anything else on the page.

Water released at the base of the tub soaks the ground you stand on and sits under the structure. In warm weather that means a permanently damp surround, soft ground and, over time, movement under a tub that needs to stay level. In cold weather it means a sheet of ice exactly where people step in and out.

So run the water somewhere deliberately, every time:

• Use a hose on the drain fitting and run it well clear of the tub and the path to it. Further than feels necessary
• Send it downhill, and never toward the tub, a building foundation, or anywhere water already pools
• Spread it out rather than putting several hundred gallons on one spot, which waterlogs ground however clean the water is
• Think about where it refreezes. Water that runs across a path or a deck before it soaks away will ice over there
• Keep it off the base and insulation beneath the tub, since standing moisture against a structure serves no purpose

If you drain regularly, it is worth setting this up once: a length of hose that reaches a chosen spot, a route that avoids anywhere people walk, and a drain channel formed in the base if you are still preparing the site.

Where the water can go

Untreated water

Water reading zero sanitizer, or a fresh fill that was never treated, is genuinely useful. Garden beds, lawn, trees, compost, or back to the lake, river or ocean it came from.

Treated water

Neutralize it first, then treat it as ordinary greywater onto vegetated ground where it filters through soil. Avoid storm drains, ditches and anywhere with a direct path to a waterway, since sanitizer is toxic to aquatic life well below the concentration you would notice in a tub.

Salt water

Back to the ocean, which is the neatest loop available. Never onto a garden, since salt accumulates in soil and does not filter out.

Water you are unsure about

Gravel, hardstanding or a lawn area you do not care about, well clear of anything growing that you do. Never a vegetable bed.

Getting it out

Plan this before the tub is full rather than after, because the method decides how long the job takes.

• A drain fitting with a hose is simplest. Gravity does the work and the hose gives you control over where it ends up
• A submersible pump is faster and can push water uphill or much further away. Worth owning if you drain often
• A siphon needs no equipment beyond a hose, provided the outlet sits below the tub
• Bailing is the fallback, and the reason people fit a drain kit after the first time

Leave the external drain valve open through freezing conditions so nothing is trapped in the fitting.

While it is empty

The only time you can reach every surface, so it is worth fifteen extra minutes.

1. Clean the interior with a soft cloth and a mild plant-based cleanser while the surface is still damp, then rinse thoroughly. Nothing abrasive, no pressure washing, no vinegar or acidic cleaners
2. Pay attention to the waterline, where oils leave a tide mark that lifts easily now and stubbornly later
3. Brush the cedar with a soft-bristle brush, working with the grain
4. Deep clean or replace the filter, by soaking rather than hosing. Starting a new fill with a saturated filter undoes most of the point of changing the water
5. Check the underside of the cover for mildew
6. Change the anodes if your tub has them and they are due

Refilling

Fill through a hose filter, then balance in order: total alkalinity 80 to 120 ppm first, then pH, then calcium hardness 150 to 250 ppm, then sanitizer last. Test again two or three times during the first week, since new water moves more than settled water.

Full detail in how to fill a hot tub, and on what your source gives you in your hot tub water source, and what it means.

How often

With filtration and a consistent routine, every three to four months. Without filtration, usually around each period of use. An ocean fill every five to seven days.

Change it sooner when water stays cloudy after balancing and a clean filter have had time to work, when foam persists, when there is a non-chemical smell, when treatments stop behaving predictably, or after any fouling event. More in when to stop treating and change it.

If you have an AlumiTub

Two things make this easier than on a conventional spa. There is no internal plumbing, no jet housing and no filter chamber, so a drain and rinse genuinely resets the tub rather than leaving reservoirs behind. And every surface the water touches is reachable, so cleaning while empty is quick.

Clean with a soft cloth and a mild plant-based cleanser only. Never vinegar, never an unapproved descaler, nothing abrasive, since the aluminum protects itself with a very thin surface layer that acids and abrasives remove.

On a Wood Fired or Hybrid, never drain below the fill line until the firebox has completely cooled. On tubs fitted with anodes, which is Electric, Hybrid and Wood Fired with filtration, the empty tub is the natural moment to change them.

The optional Drain Kit takes a garden hose and stubs out from the side, which is what makes leading water properly away straightforward. It needs a channel formed in the insulation base, so it is worth planning at the same time as the site.

Refill through the hose filter and balance to alkalinity 80 to 120 ppm, pH 7.4 to 7.8, calcium hardness 150 to 250 ppm and bromine 2 to 3 ppm and never above 3. Good Clean Living Water Care includes the tub cleanser and the filter cleanser for exactly this job.

Not sure where your water is? Check your readings.