I can't help you with your sink drain question but I may be able to shed some light on your grill problem.
The propane quick connect on our Discovery is dispensing propane AFTER the coach regulator so it is low pressure(already regulated). Your grill has a second regulator that needs to be removed, and if it can't be, you need a grill without the second regulator. I have a Weber Baby-Q and I removed the grill regulator and replaced it with a quick connect fitting.
Jim & Sandy
2011 Discovery 36J
2014 Grand Cherokee Summit