1. A liner for use in casting within a cast manhole structure having a cast base, the liner comprising:an entry aperture defining an entry aperture diameter;
a first side wall having a first pipe aperture sized and positioned to be aligned with a first side opening of the cast base;
a second side wall having a second pipe aperture sized and positioned to be aligned with a second side opening of the cast base; and
a liner top wall disposed radially outwardly of said entry aperture diameter and extending between said entry aperture and said first side wall;
a flow channel extending between said first and second pipe apertures and in fluid communication with the entry aperture; and
a liner lid received in the entry aperture, the liner lid comprising:
a first lid portion sealingly engaged with a sidewall of the entry aperture; and
a second lid portion coupled to the first lid portion and moveable in an upward direction about an axis which extends across said entry aperture between a closed configuration in which the second lid portion is sealingly engaged with the entry aperture and an open configuration in which the second lid portion is disengaged from the entry aperture.