As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties.
Emptying a water tank without a pump is usually possible if you can use gravity. The easiest method is to open a low drain valve and attach a hose. If the tank has no drain, you may be able to start a siphon through the top opening.
Both methods work only when the water has somewhere lower to flow. A large tank should never be tipped, lifted, or entered while it contains water.
Start With Gravity
Water naturally flows downhill. You can use that movement instead of a pump.
There are two common ways to empty a tank:
- Open a drain or outlet near the bottom of the tank.
- Use a hose as a siphon if there is no usable bottom drain.
A drain is usually the simpler choice. A siphon is helpful when the only access is through the top of the tank.
Before starting, decide where the water will go. Avoid sending large amounts of water toward foundations, septic systems, neighboring property, or areas where it could cause erosion.
Method 1: Use the Tank's Bottom Drain
Many rainwater tanks, IBC totes, barrels, and cisterns have an outlet near the bottom.
This is the best place to start because gravity does most of the work.
1. Check the outlet
Look for a valve, spigot, bulkhead fitting, or threaded connection near the bottom.
A bulkhead fitting is a fitting that passes through the tank wall and creates a sealed connection for a pipe, valve, or hose.
Check that the valve and fitting look secure before opening them. Old plastic fittings can become brittle.
If a valve is damaged or the tank wall around it is cracked, do not force it.
2. Attach a hose if needed
A hose lets you direct the water away from the tank.
Make sure the hose connection matches the outlet. IBC tote valves, rain barrel spigots, and large cistern outlets may use different thread and fitting sizes.
Do not force together parts that do not match. A poor connection can leak or damage the tank fitting.
3. Run the hose downhill
Place the discharge end lower than the water level inside the tank.
The greater the height difference, the more easily gravity can move the water.
Keep the hose as straight as practical. Kinks and sharp bends reduce flow.
4. Open the valve slowly
Start with the valve partly open.
Watch the hose, connections, and drainage area. A large tank can release a surprising amount of water.
If everything is working properly, open the valve farther.
5. Let the tank drain
Flow will usually slow as the water level falls.
A bottom outlet may not remove every last inch of water because the opening is normally slightly above the tank floor.
You can remove the small amount left behind during cleaning if necessary.
Method 2: Siphon the Water Through a Hose
A siphon can empty a tank even if there is no drain at the bottom.
A siphon uses a water-filled hose and gravity to move water from a higher level to a lower level.
The discharge end of the hose must remain lower than the water surface in the tank.
1. Choose a suitable hose
The hose needs to reach:
- From inside the tank
- Over or through the tank opening
- Down to a discharge point below the tank's water level
A larger hose can usually move water faster, but its size must still be practical for the tank opening and drainage area.
2. Put one end near the tank bottom
Feed one end of the hose into the water.
Keep it close to the bottom without pushing it hard into sediment. If the hose sucks against the tank floor, flow can stop.
Try not to disturb heavy sludge if you plan to use the water elsewhere.
3. Fill the hose with water
A siphon works best when the hose is completely filled with water before you start.
One simple method is to fill the hose from a clean water source, close or hold both ends, place one end in the tank, and move the other end to the lower discharge area.
Release the lower end once the hose is positioned.
Do not start a siphon by sucking on a hose with your mouth. Stored rainwater can contain microorganisms, animal waste, debris, or other contaminants.
4. Keep the outlet lower than the water
Once water begins flowing, keep the discharge end below the water level inside the tank.
If you raise the outlet too high or allow air into the hose, the siphon may stop.
You will then need to refill the hose and restart it.
5. Stop the siphon when needed
To stop the flow, you can:
- Lift the discharge end above the tank's water level.
- Remove the intake end from the water.
- Close a suitable valve installed in the hose.
Be ready for water remaining inside the hose when you disconnect it.
Why a Siphon Sometimes Will Not Start
A siphon depends on a continuous column of water inside the hose.
If it does not work, check for these common problems.
Air is trapped in the hose
Even a large air pocket can interrupt the siphon.
Refill the hose completely and try again.
The discharge end is too high
The end where water comes out must be lower than the water surface in the tank.
Factor in practical steps for draining water with no pump to assess pressure-switch behavior across normal draw cycles.
Moving it farther downhill may help.
The hose has a leak
Loose fittings, cracks, or holes can let air enter.
A siphon needs an airtight hose above the water line.
The hose is kinked
Straighten sharp bends and remove anything that is pinching the hose.
The intake is blocked
Leaves, algae, sediment, or the tank floor itself can block the inlet.
Raise the intake slightly and check it for debris.
How Fast Will a Tank Drain?
Drain time varies widely.
Important factors include:
- Amount of water in the tank
- Hose diameter
- Outlet diameter
- Difference in height between the tank and discharge point
- Hose length
- Kinks and restrictions
- Sediment or debris
- The design of the tank valve
Flow normally becomes slower as the tank empties because there is less water pressure pushing toward the outlet.
For this reason, do not assume that a tank that drains quickly at first will continue at the same rate.
What If the Tank Is Below Ground?
Gravity drainage may not work for an underground tank.
If the discharge point is higher than the water level, neither an ordinary drain hose nor a basic siphon can move all the water uphill.
A pump may be required.
Underground tanks also create additional safety concerns. Never enter a cistern or other enclosed tank to remove water, clean it, retrieve equipment, or inspect the inside. Tanks can be confined spaces with dangerous air conditions and difficult exits.
Use a qualified tank or water-system professional when entry would otherwise be required.
Can You Tip the Tank to Empty It?
Do not tip a large tank while it contains a significant amount of water.
Water is heavy. A tank holding hundreds of gallons can weigh thousands of pounds when full.
Trying to lift, roll, or tilt it can:
- Cause the tank to move suddenly
- Damage fittings
- Crack the tank
- Injure someone nearby
- Damage the supporting base
Small portable containers may be designed to be lifted when nearly empty, but follow the container manufacturer's handling instructions.
For large rain tanks, IBC totes, and cisterns, drain the water instead.
Removing the Last Water From the Bottom
A gravity drain or siphon may leave a shallow layer of water.
If you are preparing the tank for cleaning, storage, or repair, you may need to remove this remaining water separately.
Depending on the tank design, safe options can include:
- Using the lowest factory drain point
- Carefully repositioning the siphon hose
- Removing small amounts through an accessible opening with equipment designed for the job
Do not climb inside the tank.
If the remaining water must be completely removed for repair, inspection, or sanitation, professional tank service may be the safer option.
Watch for Sediment
Rainwater tanks often collect fine dirt and other material at the bottom.
Emptying the tank can stir this sediment.
If you are draining water onto a garden, avoid suddenly releasing a thick layer of sludge through small irrigation lines. Sediment can clog emitters, valves, and filters.
If the tank is being emptied for maintenance, plan to inspect accessible screens, filters, valves, and fittings once the water level is low.
Protect the Tank While It Is Empty
An empty tank behaves differently from a full one.
Follow the manufacturer's requirements for anchoring and installation, especially for tanks exposed to strong winds or groundwater.
An underground tank may also depend on surrounding soil conditions and proper installation to resist outside forces. Do not assume that completely emptying a buried tank is harmless.
If you are unsure whether a buried or permanently installed tank can safely remain empty, check its installation instructions or contact a qualified installer.
When a Pump Is the Better Choice
Gravity is useful, but it cannot solve every drainage problem.
A pump may be needed when:
- The water must travel uphill.
- The tank is below the discharge area.
- There is no practical way to create a siphon.
- Water must be removed faster than gravity allows.
- The tank contains heavy sediment that blocks the outlet.
- Complete drainage is required for professional repair or service.
Electrical pumps around water need suitable power connections and protection for the location. Avoid improvised extension cords or electrical connections near wet areas.
Frequently Asked Questions
Can I empty a water tank using only a garden hose?
Yes, in many cases. Connect the hose to a bottom outlet or use it as a siphon. The discharge end must be lower than the water level in the tank for gravity to keep the water moving.
How do I empty a tank that has no drain valve?
A siphon hose is often the simplest option. Put one end near the bottom of the tank, fill the hose completely with water, and place the other end at a lower discharge point.
Can a siphon empty the entire tank?
Usually not completely. Once the intake begins drawing air, the siphon stops. A shallow layer of water may remain on the tank floor.
Why does my siphon keep stopping?
Common causes include air in the hose, a leaking hose, a kink, a blocked intake, or a discharge end that is not low enough.
Can I siphon water uphill?
A basic siphon cannot discharge water to a point higher than the water source. The hose can pass over the top of a tank, but its final discharge point must be lower enough for gravity to maintain the flow.
Is it safe to start a siphon by sucking on the hose?
No. Do not put your mouth on a hose containing stored rainwater or other untreated water. Fill the hose with water by another method instead.
Can I tip an IBC tote to get the last water out?
Do not tip an IBC tote while it contains a significant amount of water. The combined weight of the tote and water can make it dangerous and can damage the container or fittings. Use the bottom valve or another safe drainage method instead.
Do I need to enter the tank to clean out the remaining water?
No. Do not enter a cistern or enclosed water tank. These can be dangerous confined spaces. If cleaning or repair requires tank entry, use a qualified professional.
