What is the test for asserting fifth amendment privilege in a civil case?

The plaintiffs are not "claimants" because they have alleged no specific property interest in the forfeited items. They assert that claiming ownership of the forfeited items might incriminate them in pending criminal investigations for tax and welfare violations. They contend that forcing them to choose between their privilege and their lawsuit makes assertion of the privilege "costly." See, e.g., Campbell v. Gerrans, 592 F.2d 1054, 1057 (9th Cir.1979) (litigant should not suffer a penalty for assertion of fifth amendment privilege).