Do the back taxes have to paid before transferring property to another

Yes. Also taxes which have accrued but are not yet due, should be prorated, based on the latest available figures to the close of escow. The title company can do this.

This is sort of a grey matter in my mind. If you sell this to pay your back taxes then I think it's fine. But transferring a property just for the sake of transferring it (the IRS won't like this). But what are the chances of the IRS discovering this and then taking you to court? Hmmmm, depends on how rich you are is my guess.
Do you have a reason to transfer other than tax evasion? In my book tax loopholes when the IRS finds out they were cut out of a bankruptcy deal for instance they then sued in court for the rights to collect and the IRS has a limited time frame in which to sue.
The best thing is to pay the IRS every month for your back taxes to show them you really are trying.
(laymen's opinion)