Breast Pump Troubleshooting: Milk Backing Up Into Tubes

Occasionally, we hear from moms that they’ve looked down while pumping and GASP! their precious milk was backed up into the tubes!

No one wants to see milk where it shouldn’t be. Pumping is a lot of work without cleaning an extra piece of pump equipment, and the tubes need to be kept free of moisture.

Getting milk in your tubes can be particularly frustrating because it can happen out of the blue, or start to happen after using the pump for a few months with no issues.

Trying to identify what’s causing the issue for you can also be tricky, because it’s not a standard one-pumping-answer-fits-all scenario.

Why Does Milk Get Into the Tubes?

Your tubes serve the function of drawing the vacuum from the pump motor to the flanges. If you watch the flow of milk into a breast pump flange, you’ll notice that it goes straight back and then straight down, where it flows through the duck bill valve into the collection container.

Milk only gets into the tubes when it goes straight back, straight down and then fills the chamber faster than the duckbill valve can let it out. If that chamber fills too quickly, the milk will reach the hole where the vacuum enters the flange/collection container device. To prevent milk in the tubes, we need to prevent the milk from rising too quickly in that chamber.

Keeping the flow of the suction going in the right direction is KEY to efficient pumping.


Some breastfeeding moms deal with two issues that come into play here: Oversupply and Overactive Milk Ejection Reflex (OMER). Oversupply is when a mother has more milk than her baby requires. OMER is when the milk comes out (no matter the volume) very quickly and with a lot of force…think of a fire hose. While these two challenges don’t ALWAYS go together, they very often do. Most of the moms who are dealing with milk in their tubes are dealing with one of these issues.

Is There Milk in the Tubes Because My Milk is Coming too Fast?

Milk that comes quickly, regardless of force, can quickly fill the chamber. As an International Board Certified Lactation Consultant (IBCLC), I’m usually hesitant to ask a mom to watch her breast pump. That’s because your body is designed to release milk to your baby — not a machine. One of the “tricks” that I use to help moms release their milk to a machine is to encourage moms to NOT watch the pump but rather focus on something else, particularly something that reminds them of their little ones.

BUT, if you regularly have milk backing up into the tubing, it might be wise to keep an eye on the volume of milk in the chamber and make changes in posture or even cease pumping for a moment if you see the milk rising.

Is There Milk in the Tubes Because My Milk Ejection is too Strong?

It is doubtful that OMER in and of itself would cause the milk to get into the tubing. A mother can have a very strong milk ejection with a normal or even low volume (though it is rare). The force of the milk would have to bounce off the back, bounce off the bottom and bounce perfectly into the hole for force alone to be a factor in getting milk into the tubing. However, if you have OMER that is combined with a large volume of milk, this could be the issue.

Is Fat in My Milk Making the Duckbill Valve “Stick” so That it Doesn’t Allow the Milk Through?

It is certainly possible. If you notice that milk is gathering in the chamber but NOT dripping down into the collection container, it would be wise to check out the valve. You can pop it off, examine it to see if it is “sticky” and rinse it with warm water before returning it to the pump. Making sure to rinse it off thoroughly after each pumping is always a good plan. Your duckbill valve needs replacing if it is worn or torn, it’s a good idea to have a spare parts kit on hand for this purpose.


Check Your Posture

The most common reason we have discovered for milk backing up in the tubes is that mom is leaning forward over her breast pump. The very angle of her body and how she holds the pump parts to her body can increase the likelihood of the milk volume reaching the hole leading to the tubes.

So, if milk is backing up into your pump tubes, CHECK YOUR POSTURE. Holding your pump flanges and collection containers perpendicular to the floor will minimize milk ending up where it doesn’t belong. Some mothers find this particularly challenging as sitting straight up is painful for them. Make sure that you find a location for pumping that supports your posture and, if all else fails, grab some pillows to help you out.

Pumps Up

Some mothers find that keeping their breast pump at or above chest level during pumping (as opposed to down at waist level or sitting on the floor) helps to prevent milk from entering the tubing. This should also help you see more easily if any milk has entered the tubing.

Try Turning The Cycle Speed Down and Pressure Up

Some hospital grade breast pumps have independent speed and suction controls, so you can turn down the cycle speed on the pump while increasing the suction. Try to track when you are getting milk backing up into the tubing and turn the cycle speed down on the pump during that time, while increasing the pressure (don’t increase the pressure above what is comfortable!) to allow the pump to work most efficiently. Many moms report that this fixes the issue.

Should I Try Another Flange System?

The breast pump flange/tubing system is designed to allow you to empty your breast as efficiently as possible, and that can work against some moms who release milk quickly.  If you have ruled out other causes of milk getting into the tubing, tried turning the cycle speed down, and are still having this problem repeatedly,  it’s worth experimenting with another flange system to see if that helps. Some moms report that switching to another manufacturer’s flange system does help, but not all moms can resolve the issue this way.

If you do get milk in the tubing, it is essential that you clean them well. 

  1. If you get milk in your tubing, wash the tubing in warm water with dish soap and rinse well. Do not remove the orange cap at the end of the tubing.
  2. Swing the tubes in a circle over your head (think cowgirl with a lasso) to remove excess moisture. You will probably have to do this for two or three minutes, so take a break after doing it for a minute and then repeat three times (or until you no longer can see water). Take caution when swinging tubing, it can cause injury or damage.
  3. Drip a small amount of isopropyl alcohol through the tubing to help speed the drying process.  Drip the isopropyl alcohol thru the opening without the orange cap and let it drip out the orange cap (at the bottom).
  4. Be sure to dry the tubes thoroughly by hanging them to dry overnight or for a few hours.
  5. It’s always a good idea to run the pump for a couple of minutes after pumping with the tubing attached — without the collection containers and flanges attached — to ensure no condensation has formed unnoticed.

Fortunately, even if milk does enter the tubing and make it all the way towards the pump unit itself, be rest assured that your milk cannot get into the motor, create mold inside the pump, or contaminate the mechanism.

The best hospital grade breast pump is fitted with a barrier filter protection Bacteriostatic Filter which prevents any milk reaching the inside of the pump. If your Bacteriostatic Filter does get wet for any reason, it needs to be replaced before pumping again.

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