Hey guys, after years of trying and using different systems, I think I've hit on the easiest way to automate reservoir top offs.
I pretty much always run a heavy-duty garden hose into my rooms, makes it MUCH easier to produce water in the room. I typically put them onto a 2 or 4-way splitter, so I can have a garden hose for rinsing out buckets, reservoirs, etc without using up my filters.
Once you have your line and splitter installed, pick up a Rainbird hose timer that will allow you to turn the valve ON for a set period daily. For me, 2 hours is enough time for my Tallboy filter to completely fill both of my 115gallon reservoirs.
I set the ON time to a part of the day when the pumps and timers aren't running at all, so if the reservoirs are filling they aren't pumping out at the same time. This is very important! If you set the ON time to when your lights are on and the pumps are running, you'll get floods, period. My Rainbird has a small button to activate the fill manually, which is nice for res changes and for making drinking water.
My Tallboy came with a hose end fitting for the inlet hose, so that part was easy. Lowes (or your local hydro store) carries 3/8"OD poly tubing and push fittings, so I got an array of shutoff valves and tees.
The single filter outlet runs down under my tables to a 3-way splitter:
1 line to north res
1 line to south res
1 line to drinking water/handy line.
Each reservoir has its own shutoff valve and float valve (from local hydro store) and it's ALL push fittings, no wrenches needed to connect or disconnect lines, woot!
Now I can leave my room for a week without worrying about running out of water.
If this doesn't work for your particular setup, holler and I can tell you how to do this with an inline 3/4" sprinkler valve and a programmable sprinkler timer, but it's more involved!
Hope that helps you guys out.