The threaded fittings on these are honestly really really bad. It's just how they're made, seams, undersized threads etc.
I used 4 or 5 wraps of blue monster tape followed by Megaloc pipe dope but any decent pipe dope would probably do fine as long as it's compatible with pvc etc. Don't over tighten them, just go fairly tight. If it leaks pull it back apart and add more tape is what I found works. After wrapping the tape 4-5 wraps run your fingernail down it to try and get it more in the thread before adding the pipe dope. If all you've got is the typical thin white tape you're going to need a lot more than 4-5 wraps.
DO NOT put the pipe dope under the tape it's not going to help and it's going to make a big mess and make the tape want to push out.
Honestly the Hayward ones seem to bottom out more than actually get tight.