You could take a slightly different approach and use a rule like I suggested in this thread:
In this case, I trigger when power goes over a value that suggests the machine will be in use, use a "Wait" for a value that suggests the machine is no longer in use (literally 0 didn't cut it for me, but this will depend greatly on the power reporting functions of your device--which you can also consider adjusting if needed; I prefer mine to be as non-chatty as possible while still getting the data I need), and then notify if it stays that way for some time. As usual with things like this, you'll need to adjust the values and timing to suit your particular plug and washing machine.