Unfunded Pension Liability Advice

Has anyone made an acquisition where the company had an unfunded pension liability and how was that handled at close/purchase agreement (in an asset deal)? Obviously, it represents a form of indebtedness / off balance sheet liability, but I am curious to know how people actually handled this: decrease in purchase price, some form of escrow account, seller pays off the liability directly to union, etc. Also, I already have a legal team, so I am not looking for a legal service provider -- would just like to learn how people approached this.