how do i clean the water reservoir on the flexbrew trio? it’s got this pinkish slime in the corners i can’t scrub out.

Diagnosis

The pinkish, slippery residue accumulating in the corners of your Hamilton Beach FlexBrew Trio 49902 water reservoir is a biofilm caused by *Serratia marcescens*. This is an airborne bacterium that feeds on the fatty acids found in soap residues and the mineral deposits left behind by hard water. Because the reservoir has tight 90-degree angles at the base and narrow channels where the tank meets the valve, these areas become stagnant pockets where the bacteria can anchor and multiply, creating a protective slime layer that resists simple rinsing.

You can confirm this is a biofilm if the residue feels slippery to the touch and persists even after a quick rinse with dish soap. If the slime has a slight orange or coral hue, it is definitely *Serratia*. While typically non-pathogenic for healthy adults, this biofilm can harbor other contaminants and may eventually affect the taste of your coffee or lead to a clog in the internal pump system if pieces of the slime break off and enter the heating element.

How to Fix It

To completely eradicate the biofilm and sanitize the reservoir, you must use a chemical agent that breaks the cellular wall of the bacteria, as standard dish soap often provides the nutrients the slime needs to grow.

1. Remove the Reservoir: Grasp the handle and lift the water reservoir straight up and away from the main unit. Do not attempt to clean the reservoir while it is attached to the machine, as water entering the electrical base can cause a short circuit.
2. Empty and Rinse: Pour out all remaining water. Rinse the tank with warm water to remove loose debris.
3. Prepare the Sanitizing Solution: Mix 1 tablespoon of unscented, liquid chlorine bleach into one gallon of lukewarm water. Do not use scented or "color-safe" bleaches, as these leave chemical residues that will taint your coffee.
4. Deep Soak: Fill the reservoir to the "Max" line with the bleach solution. Let it sit for at least 30 minutes. This allows the chlorine to penetrate the biofilm in the corners where brushes cannot reach.
5. Mechanical Scrubbing: Use a flexible bottle brush or a dedicated narrow-neck dish brush. Focus specifically on the bottom corners and the area around the outlet valve at the bottom of the tank. Apply firm pressure to break the physical bond of the slime.
6. Triple Rinse: Empty the solution and rinse the reservoir three times with hot water. Continue rinsing until there is no detectable scent of chlorine.
7. Dry and Reinstall: Wipe the exterior dry with a lint-free cloth and snap the reservoir back into the base, ensuring the valve is seated firmly to prevent leaks.

If That Didn't Work

• White Vinegar Shock: If the pink slime is accompanied by white crusty deposits (calcium buildup), the bacteria are likely hiding inside the scale. Fill the reservoir with a 50/50 mix of distilled white vinegar and water. Let it sit for 2 hours, then scrub. The acetic acid breaks down the minerals that the biofilm clings to.
• Hydrogen Peroxide Treatment: For stubborn stains, use 3% hydrogen peroxide. Pour it into the corners and let it bubble for 10 minutes. The oxidative action of the peroxide is often more effective at "lifting" the slime from the plastic walls than bleach is.
• Isopropyl Alcohol Swab: For the very tightest corners where brushes cannot fit, soak a cotton swab (Q-tip) in 70% isopropyl alcohol and scrub the specific pink spots. This kills the bacteria on contact and evaporates quickly.
• Replacement Reservoir: If the plastic has become pitted or scratched (creating microscopic grooves where bacteria hide), the biofilm will return every few days. In this case, purchase a replacement reservoir part specifically for the 49902 model to ensure a sanitary brewing environment.

Heads Up

• Avoid Soap Overuse: Do not use heavy amounts of dish soap to clean the reservoir. The residue left behind acts as a food source for *Serratia marcescens*, actually encouraging the pink slime to return faster.
• Fresh Water Rotation: If you do not brew coffee every day, empty the reservoir and refill it with fresh water every 48 hours to prevent stagnation.
• Dry the Tank: When performing a deep clean or descaling, leave the reservoir off the machine and upside down to air dry completely before reassembling.
• Filter Maintenance: If you use an aftermarket water filter inside the reservoir, replace it every 30 days. Old filters can become breeding grounds for the same bacteria affecting the tank walls.