I found one schematic for controlli...
[url]http://en.wikipedia.org/wiki/Dimmer
The controls I have used for shaded pole motors did not have a rectifier bridge and were similar to this phase control:
**broken link removed**
Phase control might work in your case. I know you don't want to buy the controller, so my suggestion would be to look up phase control and see whether you want to try to build one. You will find circuits that use an SCR and others that use a triac for motor control and light dimming. I don't have the experience to know whether one is better than the other.
However, the big question is what type of motor is in your pump? I suspect you don't want to tear it apart to find out. At the same time, if you make a phase control yourself and it doesn't work, you won't know whether it is the wrong technology or the way you made it that is the problem. I suggest buying a cheap one like shown in the links I provided. If it works, then you can experiment with making your own. If it doesn't work, you can keep the controller for something else, and still experiment on ways to control the motor in your pump.
John