Can you leave paint in an airless spray gun overnight?

You can leave paint in an airless spray gun overnight, but it is not ideal and depends on type of paint, how you store it, and whether you take precautions to prevent drying and clogging, with different recommendations for water-based latex versus oil-based paints. For water-based latex paint, many painters leave paint in airless sprayer overnight by relieving pressure, leaving pump in water or paint bucket, covering tip with damp rag, and keeping system sealed, and it will often be okay for 12 to 24 hours without hardening if kept cool and sealed, but you risk paint skinning, tip clogging, and pump drying if air gets in. Best practice is to clean if longer than overnight. For oil-based paints, leaving overnight is riskier because solvents evaporate slower but paint can still thicken and gum up. Manufacturers like Graco recommend if you must leave overnight, leave sprayer in paint, relieve pressure, and cover, but clean within 24 hours. If you leave longer, paint can cure inside pump, hose, and tip, causing expensive damage. To leave overnight, submerge suction in paint, wrap gun in plastic, keep in cool place, and prime in morning. For best results and to protect expensive sprayer, many pros clean same day or do quick rinse. So yes you can leave overnight with precautions, but cleaning is safer.