A while ago, a bunch of people, including myself, posted about how they dose kalk. I was using a 2 liter bottle with a hole in the side and airline tubing on my 29g reef.

Well, a 2 liter reservoir certainly wouldn't do it for my 125g tank. So, here's waht I am using now:

Take a 5 gallon water-cooler bottle. Remove the plastic cap and drill 2 holes in it, just large enough to shove in rigid plastic tubing. In one hole, put a very short length of rigid tubing. In the other hole, put a long piece, long enough to come within an inch or so of the bottom of the bottle (but not all the way. You don't want to suck the white kalk residue into the tank).

Then, use epoxy around the tubing and the lid so as to create a water and air-tight seal. Don't worry about the epoxy. Water won't be coming in contact with it. Let it harden.

Attach airline tubing to each of the rigid tubes. At the end of the airline tubing which goes far down into the bottle, attach one of those airline needle valves. This end will hang over your sump.

Place the bottle somewhere so that the bottom of it will be above your sump level.

To use:

Remove lid and fill with kalk.
put lid on.
open airline valve all the way.
blow air into the tubing which doesn't have the valve, until kalk starts to flow out of the valve. Then, adjust the valve down to get the desired drip rate.
This is basically a siphon that you don't have to drink kalkwasser to start.

If you had powerful-enough airpump, and delivered your kalk up instead of down (say to the overflow in the tank), you could hook an air pump up to the siphon-starting tube and force air into the bottle and kalk out. I wasn't able to get it to go with a cheesy pump I had laying around, but I was able to get it to go with my lungs. This would have the advantage that you could put it on a timer.