Here's the link that I used to build my doser:
DIY doser
I used the 2 gallon dispenser from Walmart (Rubbermaid - Stacking water dispenser). It was $5.82.
I bought the canula at a medical supply warehouse locally and it was $6.
Works great. For right now, I'm just tying a knot in the line to control the drip rate. I mix up 2 gallons of KW and let it sit all day and then start a drip into the inlet chamber of my sump when I leave in the evening.
The outlet to the doser is a little bit close to the bottom so I raise the front of dispenser so that the sediment doesn't get too close to the outlet.
By morning, I've dripped about 1.5 gallons (which is approximately my evaporation rate). Then I toss out the rest of the liquid and remix another batch.
My calcium is finally starting to stabilize at around 400ppm since I started the drip. Now I can start slowly raising it until I hit my target of around 440/450.