Inspired by Steves sophisticated approach
to getting this done, and lead into the right direction via many PMs from Robert (Naja002 --> many thanks!) I have started my own, of course
very cheap, water change setup.
After getting a pressurized CO2 and my cheap fertilizer autodosing, the next big time consuming thing is the weekly water change. Luckily, the room where my tanks are is next to the garage, in vincinity to water pipes.
(I am in the middle of the setup, not finished yet).
So here is how I imagine it will work: A float valve connected to a water pipe keeps the tank topped off, and a vinyl hose connected via T to the outlet of the XP3 will work as a drain. I have an unused 43 gal tank in the garage that will be catching the water for now (to be used for watering the yard).
For now, a ball valve will shut off the draining water. Later I will perhaps install another float valve in the collecting tank, so each time I take water out of it a water change will be done. Or use some irrigation timer valve for better controlled water changes. For now, opening a ball valve and watching the tank seems so much better than the weekly garden hose ritual.
So here is how it starts... a $8 ice maker connection kit, which comes with a wonderful reinforced 10ft hose, and a self-piercing saddle valve.
I am not a plumber, and had modest difficulties to get the self piercing thing to pierce (or are my copper pipes too fat?), but with lots of swearing and a drill it finally worked:
Drilled some holes into walls, pulled the hoses through, and need to connect the T to the outlet of the XP3.
And patiently waiting for the $9 float valve...