You drill the upper cap : twice for RO fittings (CO2 and water inlet). And one for 1/2" pipe and union.
2" union is weld directly on cap with little pipe piece.
The lower cap is drill twice : one for RO fitting (emptying) and one for 1/2" pipe and union.
You need drill lower cap for the float switch cable.
The lower cap is weld on directly on the lower union.
After that, you weld the two piece with clear pvc pipe (15,7" beetwen the two piece).
You need piece of enkamat 7210 for interior.
On apex, you need three outlet : CO2 valve, dosing pump and recirculation pump).
For dosing pump, I use a kamoer with stepper motor.
I use three virtual outlets for working, higher alert and lower alert.