In order to get poster paint out of your clothing you simply have to dip your clothes in water. If you do this immediately when the paint falls on the clothing then it is best the paint will leave the clothing really soon. But in case you happened to keep it for a longer time then you can first dip that particular clothing in water. Next apply the soap on where the paint as fallen and let it soak in water for at least one hour. In case you have a washing machine then turn your washing machine regulator onto the stain section. The washing machine will do the rest for you. In case you are doing hand wash then simply after an hour remove the clothing and wash and rub it on the stained part. The stain will leave the clothing very soon.