I use this arrangement. I also have a clear elbow I put on when dumping to make sure it runs clear. There is no issue when back flushing using the hose attachment since the toilet is sealed with the flush valve and there is a stack venting the tanks.
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Lou & Freya the wonder dog
2008 GMC Sierra 3000HD Allison Duramax
2019 Flagstaff 8529FL
I use one regularly.You will be surprised at how much comes out on 2nd or even third back flush dump. I did back fill to much one time only to find out the toilet flang seal was dried out, had a bit of water leak out onto bath floor. Since have replaced seal. One word of caution, DO NOT use your fresh water hose to flush with, use seperate hose only for flushing