I wash my big quilts in the bathtub.. Of course I do it once a year, in the spring. Mine don't get too dirty but I soak them in some non-bleach soap over night , rinse them, place in a plastic laundry basket with holes and it drains out, then lay them on patio chairs to dry, back side out.
These are my handquilted quilts that I treasure.
Never thought of a zippered quilt...interesting.