Transferring fluids by siphoning seems straightforward, but you can definitely do it wrong. Here are expert tips for doing it the right way.
The Dos and Don’ts of Siphoning Fluids
Published on Apr. 23, 2025
I used to own a lightweight hot tub that you could just roll into position and fill with a garden hose, but to use it, I needed to know how to siphon fluids — specifically water. That’s because the tub didn’t have a drain. It was super easy to set up, and once I plugged it into a standard outlet, it provided many days of relaxing soaks. Changing the water presented a conundrum because of the lack of a drain, but fortunately, the tub was on a deck, so I could use gravity to siphon the water onto the lawn, which very much needed it during the dry season.
According to pool pro Jeremy Yamaguchi, the problem of draining is a pretty common one for hot tub owners, and siphoning is a common solution. All in all, siphoning is a useful technique with a number of uses around the house, in the shop or on a boat. It’s good to know how to siphon fluids, and it’s knowledge that’s bound to come in handy at some point, so we asked Yamaguchi, automotive repair expert Alan Gelfand and plumber Luke Wooffindin for tips on doing it properly and safely.
Why Siphon Fluids?
Siphoning will come in handy for any container containing 10 or more gallons of water, like a storage tank or an aquarium, or is too heavy to lift (one gallon of water weighs over eight pounds). Siphoning offers a way to get the water out without having to do any lifting. It’s also the best way to empty the gas tank in your car or riding mower, to get water out of your boat or to empty your backed-up bathtub or toilet. Winemakers transfer products from fermentation barrels to smaller containers by siphoning, and property owners can use siphoning techniques to move standing water to a place from which it can drain.
Tools & Materials Needed
- Approved siphon hose or garden hose
- Approved container
- Siphon pump
Precautions
“You should never begin to siphon hazardous fluids such as gasoline, diesel, chemicals, or any other toxic substances by mouth,” cautions Gelfand. “This can lead to accidental consumption, which can cause severe health issues or even death.” Wooffindin extends this caution to hot tub water, bilge water from a boat or any other potentially contaminated water. “Mouth siphoning is old school, but it is highly risky,” he says.
Gelfand also offers these other precautions:
- Don’t siphon hot fluids.
- Provide adequate ventilation when siphoning flammable fluids like gasoline.
- Don’t use tubing that can be degraded by the fluid you’re siphoning.
- Don’t use damaged tubing.
- Never siphon petroleum products or hazardous chemicals directly onto the ground.
- Prevent cross-contamination by using containers and siphoning equipment recommended for the fluid.
- Know what it is you’re siphoning. “Unknown containers or fluids that one cannot identify may contain hazardous materials,” he says.
How to Siphon Fluids
When you siphon, you insert one end of a hose into a fluid receptacle, bring the other end to a lower elevation, suck air from the hose to create a vacuum that the fluid rises to fill, and gravity does the rest. As the fluid begins to flow, it creates its own suction force that pulls out all the fluid. Here’s how to siphon fluids in various situations:
Gas or hazardous chemicals from a tank
- Set a container approved for the fluid on the floor under the tank outlet. The container should be large enough to hold the amount of fluid you’re siphoning.
- Insert the end of a battery-powered or manual siphon pump approved for use with hazardous chemicals into the tank as far as it will go. This is no place for a garden hose, cautions Wooffindin. It will get contaminated and probably degrade.
- Insert the outlet hose into the container and push it to the bottom.
- Start pumping. When the fluid begins to flow, you can stop pumping and let gravity do the work.
- Remove the pump when the tank is empty. Hold it aloft to allow all the fluid to drain from the hose.
Pro tip: You can also use this method to siphon contaminated water from an aquarium or similar vessel.
Water from a pool, hot tub or similarly large receptacle
This is the method pool pro Yamaguchi uses to empty pools and hot tubs:
- Connect a garden hose to an outdoor faucet.
- Insert the end of the hose into the water and push it to the bottom of the container. Have a helper hold it there.
- Turn on the faucet to fill the hose with water, then turn it off.
- Kink the hose while you disconnect it from the faucet. Maintain the kink while you bring that end to a drainage area. “Two of the most important parts are making sure the end of the hose stays at the bottom of the hot tub and making sure the kink stays firm until you intentionally release it,” says Yamaguchi. That’s why he recommends enlisting a helper.
- Release the kink. As water flows, it will continue creating suction until the tub or pool is empty — as long as you keep holding the end of the hose on the bottom.
Standing water from a depression in your yard
If you can find a drainage area at a lower elevation, you can use a garden hose to siphon standing water from your yard, but in most cases, you’ll need a pump. You can use a drill pump, which creates suction by the rotary action of a drill pump, but like the hose pump, an ingenious tool that needs only water to create suction. To use one, you’ll need two garden hoses — one connected to a faucet and one that will reach from the water to a drainage area.
- Place one end of the hose you use for drainage the lowest part of the pool of water you want to drain.
- Bring the other end of the hose to a drainage area and connect it to the pump. A second hose connects the pump to a water faucet.
- Turn on the faucet. The water flowing through the pump creates enough vacuum in the drainage hose to suck the water out of your yard.
Fun fact: This pump depends on a phenomenon known as the Venturi effect. Gas pumps use it to determine when the tank is full, and it’s tine to shut off.
Common Mistakes to Avoid
The most common mistake to avoid is sucking fluids with your mouth. Full disclosure: I’ve done that to siphon gas, and the results were highly unpleasant.
Another common boo-boo is failing to keep the end of the pump or hose on the bottom of a tub or tank while siphoning. When the hose rises above the water level and air gets in, siphoning stops, and there often isn’t enough water left to restart.
Another common mistake is failing to check the siphon hose for leaks before starting. Leaks break the vacuum and make siphoning futile.
FAQ
How to stop a siphon once started?
Pull the siphon hose or pump out of the vessel containing the fluid you’re siphoning. Alternatively, raise the end of the drainage hose until it’s high enough for the fluid to stop flowing. If you’re draining water with a garden hose, you can also kink the hose.
Which fluids are best to siphon, and which to avoid?
Water is the best candidate for siphoning, and petroleum products like gasoline, paint thinner and similar chemicals are also good candidates, as long as you use the proper equipment and observe precautions. Avoid siphoning chemicals that are strongly acidic or alkaline. You could be injured by splashes, and they will quickly degrade the hoses.
What’s the fastest way to siphon a large tank?
Yamaguchi’s method for draining a pool or hot tub, described above, will work for any large container and is the fastest way to siphon.
About the Experts
- Luke Wooffindin is a licensed plumber and gas-fitter at Safeguard Plumbing in Sydney, Australia.
- Alan “Ollie” Gelfand is a European car expert specializing in German automotive repairs. He operates German Car Depot in Hollywood, FL.
- Jeremy Yamaguchi is the CEO of Cabana, a full-service pool maintenance and repair company based in San Diego, CA.
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