It is essential to use (PTFE) pipe thread tape on polymer male thread connectors (PME16B, PM20B etc.). Use a small amount and wrap correctly on the male thread.
No (PTFE) pipe thread tape or sealant is required with Pexline female swivel connectors (PF16B, PFE20B etc.). Just ensure that the shoulder of the female is directly presented squarely to a flat machined face before tightening. This avoids crossed threads and ensures a seal.