[travelin texans]

Not sure how you could get back flow plus the back flow preventer will only restrict the flow even more especially if using the el cheapo restrictor with it. Generally if there's a bfp where we park I remove it, if possible, to connect my "regulator" then put the bfp back on when we leave.
I think I'd do as mentioned & fill the fresh water tank & use from there til the park repairs your faucet.
As for the Oxygenics head, we love ours, we've actually used it on 3 rvs so far.