Are you really an expert? The pump has a threaded union screwed into it. This is what leaks. You can't put a union on this pump without screwing it in. The O-ring on the union can't save the situation.
I decided to try the tape-and-goo method. I taped the male part up and then spread the goo on it like peanut butter. I can tell it's better because the pump filled with water just about instantly when I turned it back on. I am going to go out and shut it off to see if anything comes out. That's when the pressure reverses and water comes out of leaky suction joints.
High-temp pump unions thread into the ports on a pump, but they are NOT male pipe thread units. Pipe threads are tapered, getting larger as they go in farther. The pump port is tapered as well, so yes, overtightening can actually split the pump.
The threads on a true high-temp pump union are straight, they will tighten, but don't expand as they go in, but it is the O ring that seals.
If there is a union threaded into that pump that doesn't have an O ring, it is likely one with a male pipe-thread on one side and threaded completely into the pump. Overtighten them and the male portion will be deformed if it doesn't split the port. You only make that mistake once.
You can use Teflon tape on a high-temp union as well, I always do, three wraps, as I hate call-backs for tiny drips. I also use a small coat of silicone sealant over the Teflon. I don't have leaks.
Hayward recommends against using pipe dopes of any kind on their pumps. From the manual:
Use Teflon tape to seal threaded connections on molded plastic components. All plastic fittings must be new or thoroughly cleaned before use.
NOTE - Do NOT use Plumber’s Pipe Dope as it may cause cracking of the plastic components. When applying Teflon tape to plastic threads, wrap the entire threaded portion of the male fitting with one to two layers oftape. Wind the tape clockwise as you face the open end of the fitting, beginning at the end of the fitting. The pump suction and outlet ports have molded-in thread stops.
Do NOT attempt to force hose connector fitting past this stop. It is only necessary to tighten fittings enough to prevent leakage. Tighten fitting by hand and then use a tool to engage fitting an additional 1 ½ turns. Use care when using Teflon tape as friction is reduced considerably; do NOT over-tighten fitting or you may cause damage. If leaks occur, remove connector, clean off old Teflon tape, re-wrap with one to two additional layers of Teflon tape, and re-install connector.
