Question on Tax Lien investing

[Chris Masons]

I understand how the process works but my question is this:

If a person wins a bid for a tax lien and owner doesn't pay the lien in the specified time you can start the foreclosure process. Now assuming there is a Mortgage on the property do you end up taking the house subject to what is owed on the house?

Wouldn't it be advantageous for banks to send out their people to bid and win the tax lien auctions to protect their asset?

as always thx in advancae,
Chris