APEC ROES making a gurgling sound from the drain line, is that okay?

Diagnosis

The gurgling sound you hear in the APEC ROES-50 is typically the result of "concentrate" water (the brine water containing the filtered impurities) being pushed through the drain line and into your sink's waste pipe. Because the ROES-50 uses a flow restrictor to create backpressure against the membrane, the water doesn't flow in a steady, silent stream; instead, it often pulses or creates small air pockets as it enters the drain saddle. This is a normal byproduct of the osmotic process, specifically when the system is in "production mode" to refill the storage tank. To confirm if this is normal operation, observe the system's pressure gauges. If the gurgling occurs only when the tank pressure is low (usually below 30 PSI) and stops once the tank is full and the automatic shut-off valve (ASO) closes, the system is functioning correctly. However, if the gurgling is constant—even when the tank is full—or if it sounds like a violent "sucking" noise, you likely have a breach in the vacuum seal of the drain saddle or a blockage in the waste line causing air to be pulled backward into the system.

How to Fix It

If the gurgling is excessive or constant, you need to ensure the drain line is airtight and positioned correctly to prevent air intrusion. Follow these steps to optimize the drain assembly:

1. Locate the drain saddle clamp (the plastic piece bolted to your sink's drain pipe). Loosen the two nuts on the saddle using a 7/16" wrench.
2. Inspect the rubber gasket inside the saddle. If it is pinched, skewed, or has a hairline crack, it will allow air to leak in, causing the gurgling sound. Replace the gasket if it is deformed.
3. Ensure the 1/4" drain tubing is pushed firmly into the saddle's compression fitting. Use a small pair of pliers to ensure the locking clip is fully seated over the tubing to prevent air leaks.
4. Check the slope of the drain line. Ensure the tubing runs downward toward the drain pipe without any "loops" or "humps." A loop in the line creates an air trap that causes a bubbling or gurgling sound as water struggles to push past the air pocket.
5. Tighten the saddle nuts firmly, but do not over-torque them, as over-tightening can crack the plastic housing or pinch the rubber gasket, creating a leak.

If That Didn't Work

• Check for a Clogged Flow Restrictor: If the gurgling is accompanied by a very slow tank refill time, the flow restrictor (the small plastic inline piece on the drain line) may be partially clogged. Replace the restrictor with a new 32 GPD or 40 GPD unit to restore proper pressure balance.
• Verify the ASO Valve Function: If the gurgling never stops, your Automatic Shut-off (ASO) valve may be failing. This means the system is constantly sending water to the drain even when the tank is full. Test this by closing the tank valve; if the gurgling continues for more than 10 minutes, the ASO valve is faulty and needs replacement.
• Inspect the Drain Pipe for Blockages: A partial clog in your sink's main drain pipe can cause water to back up, forcing air bubbles back up the RO drain line. Try using a plastic drain snake or a commercial drain cleaner on your sink to ensure the waste line is completely clear.
• Relocate the Saddle: If the saddle is installed too close to a P-trap or a T-junction in your plumbing, turbulence from the sink's main flow can cause air to be pushed into the RO line. Move the saddle 3-5 inches further up the pipe, away from the trap.

Heads Up

• Avoid Kinking: Never bend the 1/4" drain tubing at a sharp 90-degree angle. Use wide arcs to prevent "air locking" which causes the gurgling to intensify.
• Saddle Placement: Always install the drain saddle above the P-trap of your sink to prevent sewage gases or wastewater from backing up into your RO system.
• Leak Monitoring: Whenever you tighten the drain saddle, wipe the area dry and wrap a piece of toilet paper around the fitting. If the paper gets damp, you have a slow leak that needs immediate correction to avoid cabinet water damage.
• Filter Cycle: Remember that as the pre-filters (Sediment and Carbon) become clogged, the pressure dynamics change, which can sometimes alter the sound of the drain flow. Replace pre-filters every 6-12 months.