I have an old concrete floor with a newer pvc type drain. The floor slopes about 1.5" over 2' around the drain so I would like to raise the drain in order to level the floor to install ceramic tiles. I'm still going to ensure the floor slopes toward the drain just enough. I figure I need to raise the drain about an 1". Is there an adapter or extension I can add to fix this? Will I be able to have similar flush grate? The top of the drain is 5" diameter (4-3/4" flush grate with 3 screws) and the interior pipe is 3".

Does the "old concrete" come into contact with the PVC? Where is it located? WIll it get really wet after the tile is installed??

I don't know of an adapter. You would probably have to know the manufacturer of the drain fitting you have. Short of that an easy way to do it is get a piece of pipe as close to the same diameter of your drain pipe where the screws go. A little larger if you have to, about 1" high less the thickness of your tile (that is your desired end height right?) Then your ready to pour or lay your mortar bed. Just get the right length of screws and screw your same drain grid down. You could get some residual water under the cement when you run the shower but since you have that steep grade I think you will be all right, just be sure to keep it nice and clear. In other words when all is said and done and if the shower starts to back up, take care of it right away by snaking the drain clear. Good luck.