If you don't have an apex you could always buy a stenner peristaltic pump with two heads on it and put it on a timer. Just have to measure how much it takes at then set the time accordingly. You can find them for less than the DOS units and they are extremely accurate and reliable. Calibration is almost never done if ever. Ive personally never used one but its what Ill be going with when I decide to set up my AWC. Disclaimer, they are somewhat loud lol so you'd probably want it to be running when no one is home.