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The author obviously had lots of fun building this amazing tree watering system. An upside bottle mounted at an appropriate height in the tree stand also works, but isn't nearly as much fun.

Good idea. I used to use a gallon jug and a siphon tube to move the level-monitoring and refilling operation out to a more accessible location. The big jug also reduces the change in level over a given time interval. Mark's system eliminates the need to control the level in the reservoir. I think the tube exit needs to be above the water level in the reservior to prevent siphoning, since washer tanks are generally below the nozzles. I'd opt for the non-digital version (fewer parts, higher reliability) unless the pump exceeds the current rating of the switches. If it does, I'd keep the relay and control that with the switches. If building the digital version, you need pulldown resistors at the gate inputs that are connected to the switches, since the CMOS inputs draw no current.

Good idea. I''ve used an extra large reservoir and a siphon tube for Christmas tree watering. The level in the reservoir tracks the level in the stand, it's more accessible for refilling, and it holds a lot more water than the stand. The float-switch control system can run unattended longer because no need to control the level in the reservoir. I''d go with the non-digital version (fewer components, higher reliability) as long as the pump doesn''t exceed the switch contact rating. If it does, that 10A relay ought to fix it and no need for the transistor etc. But if you do use the CMOS, you''ll need pulldown resistors at the inputs from the switches because the gate inputs draw no current. One reason to prefer controlling the motor or the relay directly from the switches: A LITTLE bit of arcing will help keep the contacts clean (note the emphasis).