Tank Fill Function

[Staticxsoil]

I have rainwater collection at my house with tanks at the downspouts and 150 gallons of storage located in a greenhouse in my garden. I would like to be able to use float switches that in the greenhouse tanks to fill the greenhouse tanks automatically each day with the float ensuring that I don't lose water due to overflow since my greenhouse is downhill from the house. additionally I would like to prevent the pump from running if the water level is too low. I believe the water level low situation can be handled by the rain sensor function but I have not found a way to automate the filling function.
 Ideally the logic behind this function would be:
   If water level = low then run pump for 30 seconds
   if max runtime not exceeded loop.
I am not versed in python but I'm willing to try to learn