With such a low frequency oscillator you will find it works more efficiently if you increase the value of C7, alternatively make the oscillator run faster, I suggest nearer 1KHz. The reactance of C7 is more than 50 Ohms at 142Hz!
The instability I meant was actually in the 7905 itself, they contain a high gain amplifier in their control loop and if you inject a signal into it due to poor grounding, it can make them oscillate by themselves.
As your voltage doesn't have to be precise, I would recommend you use a Zener diode to stabilize the voltage. Connect the pump output through a resistor then clamp the voltage with the Zener to ground. It will give you better stability than just using the pump output alone. Calculate the resistor so the Zener passes about 2mA when the load on the pump is as high as it will ever reach, the diode will then drain remaining current if the load decreases.
I don't think there is an English way to describe the way you built it "up in the air" is as good anything!
Brian.