Grayson, 28, joins the club from Pitching In Northern Premier League side Grantham Town.
The striker has also featured for Frickley Athletic, Mickleover and Buxton.
Waldock joins the list of players that have recently followed the route from Hillsborough to Northolme, following in the footsteps of Ben Hughes, Cieron Brennan and current player, Isaac Rice, all of whom have donned the blue and white stripes of Sheffield Wednesday prior to wearing the blue of Gainsborough Trinity.
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