Town boss Russell Slade named four trialists in his side, as he looks to further strengthen his squad ahead of the start of the new season.
Ben Davies was named as the captain for the starting Xl.
Just like on Tuesday night at Bideford, Town again raced into an early lead as Harry Cardwell turned his man and buried the ball in the bottom corner of the goal.
The Town frontmen were beginning to cause the hosts a lot of problems and when Ben Davies found Adi Yussuf, the striker used his strength to beat his man but his well hit shot rattled the Tavistock crossbar.
Soon after it was Tom Boalrinwa who found a bit of space, unfortunately his volley drifted just wide.
Tavistock did threaten briefly, but a great tackle in the box from a Town trialist centre-half denied them.
But on 41 minutes youngster Jack had doubled Town’s lead, as he beat the keeper with a powerful header from the edge of the box.
Half-Time: Tavistock 0-2 Grimsby Town
Soon after the break it was three, and it was that man Harry Cardwell again, as he latched onto a through ball from Summerfield to calmly slot home.
Russell Slade again made the changes on the hour, with Clarke, Collins, Mills, Dembele, Berrett, Kelly, Jones, Rose, Vernon and trialist coming on - replacing Davies, Keeble, Summerfield, Bolarinwa, Osborne, Yussuf, Cardwell, and the three trialists.
Seconds after Dembele's introduction, he was on the score-sheet again. The youngster cut through the home defence to ease the ball past the hapless Tavistock keeper.
And Town hardly had time to finish their goal celebrations for the fourth goal as Sam Jones was tucking away the fifth from the penalty spot, after Cardwell had been upended in the box.
On 73 minutes the home side pulled one back from the penalty spot, after a Tavistock players was fouled in the box.
Sam Jones bagged his second of the game on 82 minutes, as he tapped home from two yards.
There was still time for Scott Vernon to bag his first of the game, and Town's seventh.
Town Startin Xl: Killip; Davies, Keeble, trialist, trialist; Bolarinwa, trialist, Summerfield, Osborne; Cardwell, Yussuf.
Subs: McKeown, Clarke, Collins, Mills, Dembele, Berrett, Kelly, Jones, Rose, Vernon and trialist