At the end of the season prior to putting the camper away for winter I suddenly got a leak coming out of the rear of the TC. It was too cold to do anything about it so I drained everything and waited ...
I've fixed leaks in plumbing by just using the appropriate PVC or ABS cements. If it's a crack, fill it with the glue and then apply a couple more layers. For a stronger fix, cut a suitable coupling long-ways and apply it as a patch.