mooooks, assuming you copied evan's front-end code, the byte being sent should be a 0 or 1. the code I posted in reply#11 takes this byte and puts it into "pump_OnOff".
after that it should be a matter of doing a:
digitalWrite(outputPin, pump_OnOff);
I don't have my arduino on me, so I can't test this. if the above doesn't work you may need to tell the compiler "look man, I know the value in pump_OnOff is only ever going to be 0 or 1":
digitalWrite(outputPin, (boolean)pump_OnOff);
Hope this helps,
Brett