Overflow fitting (L), Fill/Drain fitting (R)

The Fill/Drain Fitting has a barbed fitting on the bottom-side, for connection to your submersible pump using standard 1/2" tubing.  The Overflow Fitting is designed so you can use your own preferred length of 1" flexible pipe.  You choose the length of the pipe so that it drains neatly back into the reservoir.  

Also, another great feature of the Fill/Drain Fitting is that it is designed to be used as reservoir drain. SImply pull off the top screen, insert a length of 1/2" tube into fitting, place other end of tube where you want reservoir to drain and turn on pump.  Voila!  You can now drain your reservoir without having to heave it or lug it or dump it on your shoes.

How do they work?

• These fittings work in conjunction with the submersible pump inside the reservoir. 
• The fill/drain fitting sits in the middle of tray, with the top screen where your plants are, and the bottom underneath the tray connected to your submersible pump.  When your pump turns on, it pumps the nutrient solution up through the Fill/Drain Fitting (the smaller, teal colored fitting).
• As nutrient solution is pumped into the tray, the nutrient level rises to the top of the Overflow Fitting, which then allows the nutrient solution to continue its recirculating flow back to the nutrient reservoir.  If you had no Overflow Fitting, the nutrient would go over the top of your growing tray and onto the floor...this is bad (not to mention dangerous).  It is recommended to let this overflow continue for about 15 minutes (may vary depending on your growing situation) to sufficiently feed the roots with plenty of nutrient, water and oxygen.  You can adjust the timing with an electronic automatic timer for your pump.
• Finally,  when the timer turns the pump off, the nutrient solution fully drains back through the Fill/Drain Fitting and back into the nutrient tank, until the next time the timer turns the pump on. 

When the nutrient drains from the root zone, this pulls fresh air and oxygen into the root zone -- one of the basics of Ebb/Flow hydroponics, sometimes called Flood/Drain.