I use Valterra's EZ Coupler line of sewer fittings.
90 degree elbow. This is actually two parts. One part stays attached to the sewer hose.
Sewer sponge ring or rubber ring. I use this to make an airtight seal.
If the connection at the campsite is threaded I use this threaded adapter instead of the sponge rubber ring.
This is a spare part (already shown connected in photo #1). I carry two of these. The threaded adapter stays on one and the rubber ring stays on the other.
With these parts, I haven't come across a campsite hookup that I can't connect to properly.
What works best for you?