The shower drain is a surprisingly complex device consisting of three separate pieces. the first piece goes under the shower liner, and actually attaches to the drain. The next is a ring that clamps the liner down on top of first pieces so that no water can get underneath the liner. This second piece also has a few ‘weep’ holes in it, which are very important, and allow any water that gets to the liner, to actually drain away, and not just be trapped by the third piece. The third piece is what you actually see, and is threaded into the second and is adjustable in height to match the depth of your base and tile.
The weep holes need to be protected from the mortar, else they would clog and become worthless. Typically this is done with some pea gravel, or some broken tile or tile spacers. However when I was ordering my liner cornersI noticed that Noble has a Positive Weep Protector. Since I didn’t have any pea gravel, or spare tile spacers, and the sharp edges of broken tile scared me, I decided that since it was only a couple of bucks I’d try this out. Its just a piece of clear plastic, that has ridges in it which would allow any water to flow underneath the mortar and get to the weep holes. Seems like a good idea, but since I couldn’t find anyone who knew anything about it, I figured just to be on the safe side I’d toss a few tile spacers on top of it, as some added protection.