(a) Use a teflon tape sealant or (b) a thread paste sealant. The right sealant for threaded joints is non-hardening, compatible with plastic and doesn’t add slipperiness to encourage over-torquing.
Screw pipe or fitting into Ball Valve.
Do not over tighten. The recommended way to assemble a Ball Valve is finger tight. Tighten until firm with spanner or pipe grip. One to two turns should be all that is required.
Turn handle clockwise slightly.
Put fingers under handle and pull whilst pushing with thumbs on body of valve.