By back flow valve, I assume you mean you had a vacuum breaker in the line with the hose that is attached to the tank rinse. The vacuum breaker worked as designed - water pressure keeps it closed. If there is a loss in pressure (either because of a pipe break or if you turn off the hose bib, it opens up to relieve the downstream pressure.
If you take out the vacuum breaker and there is a pressure drop anywhere upstream, then the water from the tank rinse could flow back into the RV water system instead of out the vacuum breaker and onto the compartment floor. I would not take the chance of contamination.
How about adding a length of hose between the rinse connector and the vacuum breaker and another length between the vacuum breaker and the hose bib. The extra lengths of hose would be long to let the vacuum breaker hang outside the wet bay while you rinse. That way, when you turn off the hose bib, the water will dump out of the vacuum breaker onto the ground. You can leave the extra hose attached and just tuck it into the compartment for travel after it drains.
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