I use one of these guys, although I've never used the serial connection because I'm just calculating with steam-engine anyhow and don't have disposable income to build a liquid metering system. Would be cool though, pretty easy other than the actual metering part. The professional systems have a ton of tubing and peristaltic pumps and such.
https://www.amazon.com/GF-3000-Precision-Balance-Couting-Jewelry/dp/B00G0PQN78