Hello billylee61 and

We are glad to have you join us here and we look forward to reading of your adventures and experiences. I am sure you will enjoy the website and forums. Good luck and keep us posted.
The check valve(s) is on the back of the tank. As mentioned by stern, you should have some way to access this area. To be more helpful, we need to know the year, make and model of the coach. You could include this info in your user signature by clicking on the "User CP" button and clicking on "edit signature" button.
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Mike, Certified Master RV Technician
Amy, RV Merchandiser; Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser w/ Banks & 2 toads