Update: 06/11/2015: Added two models for the use on a compressor instead of using water.

My little niece complained about her bubble bath not having enough bubbles!
So what can the good uncle do about it?
Add an air pump and bubble stone? - Takes far too long...
Take a hose from the compressor instead? ;)

No, I decided to make a little venturi nozzle!

If you have no clue what that is check Wikipedia.

There are quite a few 3D models available for Venturi systems but they are either meant for the use with compressed air or need far too much water.

I wanted something that not only sucks well (sorry for the bad joke!) but also provides a lot of pressure on the outlet so the bubbles are dispersed properly.
After a few not so good ones I now have a little nozzle that is strong enough to deflate a soda bottle, don't have a vacuum gauge at hand but it really sucks enough to feel it on your finger when closing the air vent.

What can I use it for?

Of course to make bubbles in your bath ;)
If you need a bit of vacuum, for example to degass resin, you can do this not without an expensive pump.
Basically for everything that needs decent suction....

Disclaimer:
I only provide the files and assume you know what you do with the nozzle!
I am not responsible if your printed nozzle fails due to poor print quality.
I am not responsible for any damages you cause to yourself or others if you don't use the nozzle as intended!

Here you can see it in action on a 1.25L soda bottle:

Step 1: The Models

Venturi Nozzle 10mm Hose by Downunder35m on Sketchfab

You can download the STL file directly.
For the printing I recommend a fine nozzle and 2 perimeters, 40% infill.
ABS is prefered but PLA should work the same.
No support required but a wide brim is recommended so the air vent will stay on the build plate.

Please note that this design is meant to be used submerged!
The barbed fitting is for a hose with an inner diameter of 10mm, like found for most cheap shower adapters for the bath tub.
The nozzle might still work if using outside the water but the full potential only comes under water.
If you have a good pump on your fish tank it might be a nice addition to get a strong current and more air in your tank.

Here is one directly for a standard 12mm garden hose:

Venturi Nozzle12mm Hose Fixed by Downunder35m on Sketchfab

And last but not least for those people who don't like hose clamps:

Venturi Nozzle12mm Hose Fixed Quick Connector by Downunder35m on Sketchfab

This one will fit on most if not all quick connectors for the garden hose, don't want to put names here but you know what I mean;)
Please add the rubber ring in the to groove otherwise it will leak!

Last but not least (and due to the requests) two nozzles for compressor use.
Edit, 07/11/2015: I checked the nozzles and the smaller one had it's inner diameter too much reduced during the printing - I will rectify this over the weekend.
The bigger one works good with medium air pressure but fails at pressures over 6bar - I will rectify this too to make sure maximum suction is reached around 7bar with no break down in suction if the pressure is higher.
Turns out theory does not always meet reality when it comes to 3D printing :(

The standard quick fitting should suit most hose connectors out there.
First is with a quite big inner diameter and requires a high air flow.
The second can be used on compressors with less air supply rate, like most compressors on a home level.

Air Venturi1 1 by Downunder35m on Sketchfab

Air Venturi1 1-smaller Inside by Downunder35m on Sketchfab

Step 2: Tipps for Best Stability and a Smooth Surface

As we deal with quite some pressure here, the last thing we want is our printed nozzle to desintegrate during first use.

PLA works quite good as long as you only deal with cold or warm water, for hot water ABS is a must.
ABS also allows for an easy fixing with Acetone.
The usual way is by putting the sanded part into a sealed container with a bit of Acetone and to wait anywhere between 15 and 60 minutes to get a reall smooth and shiny surface.
I don't really like this way as small details and fine structures can suffer quite badly.
Instead I use a weak ABS-juice and a brush.
With only a few coats the surface is perfectly sealed and smooth - much faster than the vapour method too.
Another way for the initial sealing is to simply (quickly) submerge the part in Acetone and to use compressed air to blow the excess of and out of small cavities - I don't like this method as it requires good timing and I don't like blowing Acetone everywhere.

The connector for the air hose is quite long on pupose.
I wanted to be able to use the nozzle in other ways too, so for max stability either push the air hose all the way up or cut the air intake a bit shorter.

Step 3: A Little Safety Note

These nozzles require quite some pressure to provide enough suction.
This means without a hose clamp (if you don't use the version for the quick connector) there is the risk that the nozzle will pop off the hose.
The water stream that comes out is also quite powerful due to the small diameter and pressure - please do not aim at people or animals!