It's turning out to be very difficult to keep up the air-tightness, now that we've got various other trades involved. As well as the Proclima air-tightness tapes that you've seen in previous posts, sealing of cracks and around pipes etc is done with Orcon F (not sure what the F stands for), a green-coloured sealant that's applied using the same type of gun+nozzle as you would apply eg bathroom sealants.