How to stop gurgling/gushing sound from a drain hose?

Question

I'm in the process of building an NFT hydroponics system that includes drain hoses connecting the growing channels vertically. They are the black corrugated hoses in the picture below and the noise they make when water is draining through them is quite loud.

I've tested the system for leaks by emptying a pitcher into the topmost channel and while admiring the dry floor I've got annoyed by the gurgling sound the vertical hoses made. To mitigate the noise bamboo sticks were added temporarily so that the water does have something "to grip onto" with surface tension and drain consistently instead of in waves. Channels were also cut into the fitting to lower the water level in the channel and make the bamboo stick more effective.

Those measures helped but did not mitigate the sound. Most solutions I've found on the web were for PVC pipes integrated into walls which are not applicable for my problem.

During normal operation, a pump would circulate the water with a constant flow rate which would help with constant drainage instead of the "waves" from the pitcher but the gushing sound from inside the pipes will not be fixed by that.

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How could I fix my noise problem?

• Spiralling the hoses to create a shallower slope?
• Stainless steel/plastic chain inside the hoses as "rain chain"?

Changing the position of the hoses/fittings is not possible because of the cost implications of replacing all the channels.

Answer 1

I suspect the drain lines are not full, i.e. there's always airspace in them, and that is what leads to non-laminar flow and noise. Add to that the fact that you have a straight vertical drop, which gives the water a lot of kinetic energy, and noise there will be.

Perhaps you could use longer sections of drain hose and form them into a helix?

Answer 2

You might test the pump. It's possible a "slow constant rate" will do just enough to mitigate your problem.

I believe your main problem is that the drains are too small, so rather than water running smoothly down the walls of the pipe while air flows back up the pipe, water is collecting to the point that it blocks air, and there is your "glug, glug" sound.

As such, you'll probably want to remove the partial obstructions you have introduced into the tubes, or replace them with something like a hollow braided rope in the hopes of maintaining airflow. But I'd start with just removing them, and then pumping at a constant rate, and adjust the rate to attempt to avoid a flowrate so high that water "bridges" across the whole cross-section of the tube, causing bubbling.

Either that, or larger drains.