Hi Nicole, your pump and filter appear to be an AstralPool blow-molded Millenium model with multiport valve on a monobloc (made in Spain), we have the same model series (our filter cannister is larger) and it seemed to me that most, if not all, of their piping is 1.5" although perhaps their threading is metric! Maybe someone has actually measured it or contacted AstralPool and asked them ( www.astralpool.com ) I've sent them a request since I'm also curious about our setup. If they respond, I'll post here.

Out of curiosity, is your pump like ours, the dual speed unit (SENA pump model SEN1815 with a "Vernis Motors" electric motor)?

Alex in OK