A double crease in a pair of pants can usually be removed by simply washing and drying the pants. The pants should be ironed in a new pattern after drying and the creases should not be emphasized in the new ironing pattern.
Pants that have stubborn creases or are not able to be ironed easily should have starch applied to them before they are ironed. If a crease is still present after washing and drying, starch should always be applied and the iron should be set on the highest temperature possible. The crease can be ironed flat with the help of starch.
Particularly deep or stubborn creases may not come out with simple washing and ironing techniques. While these are the best to use, more unorthodox methods should be used to help eliminate the creases. A bar of soap run along the crease of the pants before ironing will work on extremely creased pants. A mixture of one part vinegar and one part water can be sprayed on the pants prior to ironing, but the pants will probably need to be washed after the ironing process. Hair conditioner can be rubbed on the crease of the pants before putting them into the washer.