I've looked under the trailer to see how it drains but the panel prevents me from getting a look at it. I've also asked a dealer close by how the tanks actually are designed and they couldn't give me any help. There isn't a flush kit on this model so that doesn't help either. It's not that I need to empty completely each time it's just that after each use it will sit sometimes for a month or even more without using it. By giving my year and model I was hoping to hear from someone with the same but all your suggestions have been good. Thanks.