This is a how to for building a loud foghorn from easy to get plumbing fittings and an inexpensive double acting air pump, the idea was to emulate the hand operated type used on small ships until the 1950's shown in pic 2.
Step 1: What you need
Here are the basic parts to make a noise
A hand operated pump, a sink waste trap and a rubber glove (for the diaphragm)
Step 2: Preparing parts
The trap needs the down tube cutting off 1mm above the level of the outer edge, this cut needs to be accurate as this is where the diapragm will go so make sure you smoothe the cut edge with emery cloth.
I cut the bowl down to size by cutting a section out and sticking the 2 end parts back together. drill a small hole in the back of this part so that it isn't fully sealed.
Step 3: The noise maker
Cut a circle of rubber from the glove that is just bigger than the size of the o'ring that seals the bowl, lay it on to the o'ring joint face and trap it with the o'ring before winding on the bowl.
At this stage if you blow into the side of the fitting you will make a noise :)
Step 4: Attaching to the pump
I am fortunate as I have a lathe and turned up the adaptor from a piece of plastic, but an adaptor can be made from standard plumbing plastic fittings glued together, the main thing to remember is to have a short length of the connection tube that comes with ther pump glued into one end to allow the adaptor to be screwed on and off (allowing the pump to be used for its original purpose).
Step 5: It should now work
With the parts assembled you now have a working horn and could leave it right there......
Step 6: Making it lower and louder
This where you can go mad! Get as many plumbing parts as you can screw and glue together to make the sound path long and wider.
I added a second sink trap........