Hi! I am about to install a shower drain.This will be on a cement slab. What should the flange part of this drain touch; the existing slab or the new membrane? Thanks! Eddie:)

ARe you rolling a membrane liner over the concrete and then pouring concrete into liner pan.. If that is the case then I usually have my flange 1/2" lower than the concrete floor and roll my membrane into the drain... does this make sense..

Here, click on this... has great details on how to install a shower pan

How to Build a Shower Pan

Ballengerb1 left this at another post...maybe it can help a little more.