2014 Cedar Creek won't drain

The dealer and Cedar Creek says for me or them to replace the Hepvo trap under the shower with a standard P trap. I can't see how a trap under the shower will help the kitchen sink drain out when the holding tank is completely empty. I have ran water down the vent from above and it flows fine. Since I don't know anything about my plumbing would you explain how replacing a drain trap under a shower will fix water not going down in the kitchen sink? Sorry I'm one of those guys that trys to fix things myself instead of dragging the rig 120 miles everytime there is an issue. What I was asking for was if anyone else has had this problem with newer Cedar Creek production because they just started using the new Hepvo valve around the time mine was built. In fact the Cedar Creek engineer didn't know they were installing them.