Yes, very easy. Walk through the glass tunnel, past the hotel and to the lifts in T1. Then go down to ground level, exit the lift to the right and the path from T1 to T3 is 100 yards long. Luckily given the Manchester weather right now, it is covered like long bus shelter. You will enter T3 on the ground floor. Just go up the lifts to your right of the stairs and the walkway to T3 long stay is right in front of you.

The tunnel starts in T2 departures. I took this picture at about 1500 yesterday (to show on a whattsapp chat that the place was dead!)