I use this system (sometimes) instead of smashing out concrete to accomodate the Kerdi drain. It should only be used in basement showers and isn't a standard way of doing a shower-pan .... just an optional bit of information that may one day prove useful.
I've attached the new drain as low as I can possibly go without breaking concrete. The drain is assembled except for the adjustable screen.
Screw the top section in all the way and tape the holes.
Build your mortar bed as you normally would using the top of the drain as your lower screed.
The mortar bed is finished and set.
Remove (unscrew) the drain cover. Vacuum away any loose sand.
Begin installing the Kerdi membrane. As you can see here, I've already cut my hole just large enough to accomodate the threaded section of the drain cover.
Finish applying mortar being careful only to cover the area up to the perimeter of the drain cover.
I've used a caulking which I normally use for Wedi board installation called Sikaflex-201
Use lots so that it pushes down over the weep hole of the drain.
Finish installing the Kerdi membrane and make sure to have full contact with the caulking. This will give you a completely waterproof shower pan.
Install the drain cover making sure to allow for the thickness of the tile.
Now remember ... this isn't how the manufacturers of Kerdi (Schluter Systems) recommend having their product used (without their Kerdi drain). Regardless ... I do it when I need to, and it works.
For example when a shower drain isn't centered, but more into the corner ... it can be impossible to install a Kerdi drain because of its wide circumference.