The Saints, who had picked up the full five-point haul in Italy last weekend, repeated the dose as a penalty try plus further scores from George North, Kahn Fotuali’I, George Pisi, Ben Foden and the two try trebles secured a handsome victory which was their biggest in European competition.
Stephen Myler added four conversions with man-of-the-match James Wilson kicking two as part of a supreme display.
The visitors had started brightly, but once Northampton began to turn the screw up front they quickly found themselves on the back foot.
Referee Pascal Gauzere had already warned Treviso for pulling down a rolling maul, and did not hesitate to head behind the posts when they collapsed a scrum as the Saints advanced ominously towards their line.
The second arrived quickly, a clever move down the blindside saw Fotuali’I free Wales wing North and touch down.
Fotuali’I turned from provider to scorer for the third. There had appeared little danger when Treviso sent a clearing kick deep downfield. But the Pisi brothers combined to cut the defence apart, with the scrum-half turning Edoardo Gori to finish off the flowing move.
Just one more try was needed for the bonus point and, with Treviso down a man after lock Marco Fuser’s sin-binning, it duly arrived just before the break with North beating several defenders on an infield run before producing a wonderful one-handed pass which allowed Ken Pisi to cross for his first.
His brother got in on the act early in the second half, finishing off more sharp backline play to dot down shortly after North had departed the fray with an injury, before Ken got his second.
Full-back Wilson produced a brilliant pass as he was being bundled into touch and found the grateful Samoan, who finished from close range.
With the job done Saints were in full flow but were frustrated in their search for more tries when Courtney Lawes had a score chalked off for a double movement.
However, it proved only a brief reprieve for Treviso as their tiring, stretched defence could not prevent Manoa crashing over with one of his first touched after coming on as a replacement.
The powerful forward quickly added to his tally with a wonderful solo score. Manoa spotted in midfield and surged through it, stepping the final would-be tackler on his way to the line.
He then completed a 12-minute hat-trick when another purposeful rolling maul rumbled over the Treviso line, with Ken Pisi rounding off his own treble moments later.
Foden completed the rout by scooping up a loose ball to canter down the right-hand touchline for an easy finish.