A tangential flow filtration assembly having a filter holder, a TFF cassette, and a hollow elongate port adapter. The filter holder includes a pair of compression manifolds, with at least one of the compression manifolds having an outer surface, an inner surface, and a port leading to a fluid pathway from the outer surface to the inner surface. The TFF cassette, functionally engaged between the compression manifolds, utilizes a single filter plate comprising an ultrafiltration membrane disposed within a substantially planar framework. The hollow elongate port adapter has an engagement side and an insertion side with a flange disposed therebetween. An elastomeric sealing element is disposed in the adapter's insertion side. The hollow elongate port adapter is inserted through the port into the fluid pathway such that, (i) the furthest end of the insertion side is flush with or slightly recessed under the inner surface of the compression manifold, (ii) the flange is seated on the port, and (iii) the elastomeric sealing element forms a substantially aseptic water-tight seal within the fluid pathway.