We use the grey "threaded" elbow similar to the red one but it's in two parts. We have only been in one park EVER that we could have threaded the thing into. And we have been using sewer hookups since 1987. We just set it in place and put the sand bag over it.
Because it is stepped, it generally just wobbles around in the pipe (which tends to only be threaded to accept the pipe cap). The sand bag holds the elbow flange tight to the pipe to prevent smells. I also have a foam donut for the "large" pipes and the places the require a foam donut. The elbow will slip into the foam donut and seal tightly. I still use the sand bag. I bought both the elbow (part of a sewer hose kit) & seal at WalMart.
We jerked the yellow wire thingy off and replaced with large wormscrew hose clamps after the first time we replaced the hose.
The donut was bought to drain the food carts grey water into the campground sewer.
Currently the sewer hose is clamped to the bus drain with wormscrew clamp. It works well except it wants to cut the sewer hose. This works because we are parked and do not move. We need to replace that method before we are ready to move the bus. We only have PVC pipe and we need to put a threaded end on the pipe and a mating thread on the sewer hose. We will also be replacing the sewer hose before we leave here. It's been sitting out in the NM sun since 2011 when we moved over here. As long as we don't move it, it will hold together. Once we move it, the plastic will crack and split. Under normal moving, a "heavy duty" sewer hose from Wal-mart will last us about a year. Although we do carry an extra (unused) hose just in case. I have discovered park workers have "weed-eated" my sewer hose more than once. It's why I like using the plastic rain gutter as a sewer hose support.
(sorry for the overly large pics... I can't figure out how to make them smaller)