Washing sails, particularly sails made from hard sailcloth, such as polykote, is difficult without introducing creases and folds. Often just rinsing the sails is sufficient and this is best done by hoisting them on a calm day and spraying with a hose. Might be worth spraying the top while it partly hoisted to make sure it is throughly rinsed. Scrub off any obvious mud and dirt and then leave them hoisted to dry.
Sails should be rolled, mainsails at right angles to the leech so the seams and battens are parallel to the direction of roll. Jib can be rolled at right angles to the leech or the luff.