I have a new tiled shower going in were a tub used to be I am putting in a adjustable pvc flange how do I set it so its at the right height when I put in my tiles. I will be putting in a layer of mortar that is sloped then rubber membrane then another layer of mortar then tiles. What is the easiest way to install this so I have it right the first time.:)

The shower pan will go down first. First you install a flange type shower drain,(see image) to descrie it it is a drain that has the regular top drain with the chrome strainer, below that you have another drain It is about six inches in diamiter and the top part of the drain screws into this bottom part. This bottom part of the drain has another part that is either bolted down or it also screws together, so actually there are three pieces to this drain. The very bottom part goes down over your drain pipe, the rim of it should be level with the concrete floor, it would not hurt if it was one quarter inch lower then the floor. After you have this on and it is sealed to the drain pipe you they cover the shower floor and up the walls with a vynal sheet of plastic.
This should roll up the walls about 8 inches but you can make it as high as you want. You do not cut the corners but fold that similar to the way you would wrap a package, this way the plastic with fit snug into the corners of the shower. Secure the plastic to the walls of the shower with staples or nails, do this as high up on the plastic as you can, you might use somekind of bushing material, like the little roofing disk so the plastic willonot tear out of the nails or staples as you are working on it. After you have the vynal in place cut a hole right in the center of the drain. Make a small hole at first, then enlarge it to expose the threads that the second part of the drain will go into. Of if it is bolted down make sher all of the plastic is under the second flange. Tighten this ring tight to the bottom part of the drain. Now screw the third part of the drain into the second part and adjust the height to how thick you want you Quickset or mud for the tile or what ever you are going to cover the floor with. Make sure you have a sloope in all directions toward the drain.
Doing it this way any water that would ever get through the floor of the shower would be caught in the plastic and the drain is built to let this water drain into the sewer drain.
If you had one of the double seepage drains in your hand it would be very easy to understand all of the above. Click on; Mortar Bed Shower Floor for Tile Showers
For pictorial instructions.
Read and study before you begain. Good luck, Tom