Buy a detergent specifically intended for fine garments.
Fill your sink or basin with lukewarm or cool water, depending on the garment's washing instructions. Add the recommended amount of fine-garment detergent to the basin.
Briskly run your hand through the water to distribute the detergent and generate suds.
Submerge the sweater and gently squeeze the suds through it.
Let it soak for 20 minutes.
Drain the sink and rinse your sweater with lukewarm water until the water rinses clear.
Gently press water out of the sweater and place it lengthwise on a clean, dry bath towel.
Roll up the towel. Press with your palms to squeeze out excess water.
Remove the sweater from the towel and smooth it out so it is back in its original shape.
Lay the sweater flat on a dry towel and let it air-dry, or use a drying rack if you have one.