The present disclosure relates to modular purification systems using removable purifier cassettes for purifying liquids including, for example, liquids used in semiconductor manufacturing. A purification system may include a removable purifier cassette having a purifier inlet port and a purifier outlet port, and a manifold assembly. The manifold assembly can include a plurality of connection systems to that provide manifold ports to provide fluid to/from the cassette. In some embodiments, the connection systems may use connection nuts that can provide 360 degrees of thread engagement with less than 360 degrees of rotation.