It's a simple idea, but it serves me well for dripping kalk into my 30G tank.

Pieces:

Thoroughly washed milk jug
Garden hose extender. Used for attaching two hoses together. It has male threads on both ends, and a valve in the middle to control the volume passing through the hose. You can get these at pretty much and hardware, or garden center.
Glue/epoxy etc.
Cost:

1 gallon of milk ~$2.50 ;)
Extended ~ $3
Glue/epoxy ~$2
Cut a hole about the size of a quarter in the bottom of the milk jug. This is where you will fill the jug, and it allows for the water to flow. Next, attach the extender to the spout of the milk jug using the glue or epoxy. I used the two part epoxy that you mash together into a putty because it holds the extender nicely until the putty hardens. Voilla.

Usage:

To use this device, fill it with kalk, and set it over the tank. I usually drip it into an old Skilter that I have hanging on the tank for waterflow, and carbon bags. The valve can be adjusted to controll the drip rate. It's a little tricky, but you can get the drip rate to about 1 drop/ 1-2 seconds. This device is also a good indicator of the quality of your Kalk, if it stops dripping, it is likely that you didn't siphon the best part of the Kalk and you've got precipitate blocking the valve. Just hold the device over the sink (being careful not to shake up the precip), and open the valve for a second. You'll notice a milky white precip coming out of the valve.

Ehancements:

Use a twist tie and old pantyhose (clean ;) as a filte rto drip the water through. Attach a small tube to the valve and place the device above the tank so that the kalk drips through the tube into the tank. This allows you to place the device wherever you like.