Hamstrings

When you tuck your pelvis, it does indeed create slack in the hamstrings. This, however, is not a good longterm solution. It may help to relieve inflammation at an inflamed attachment point of the hamstrings, but for the longterm you want to lengthen the hamstrings, not let them adapt to a still shoter resting length. 

To get out of this downward spiral, progress slowly. Tuck less and then still less, until you are no longer tucking and your hamstrings tolerate the extra baseline length. Now continue further in this direction with pelvic anteversion (tipping), whcih is the opposite of tucking. (Note: do not do this by sticking your butt out). you will slowly be working your way to healthy, long hamstrings. The natural way to really lengthen your hamstrings is to learn hip-hinging to bend - get a teacher to guide you on this and again, do it very gently, gradually increasing how far you hip-hinge.