You must wash your wool cover prior to lanolising but there is no need to wait for it to dry.
Lanolin is a natural wax produced by sheep to protect their skin and wool from the environment. It hinders bacterial growth, has natural odor fighting properties and protects wool's unique qualities including moisture regulation.
Mix 1/2 tsp of lanolin in a 1/2 cup of boiling water until it's dissolved. Top up with cold water until the water is just warm and then submerge the cover and squeeze to push out the air bubbles. Leave it to soak for about 1-2 hours. Gently press out the water with a towel and lay flat to air dry in shade. Once dry, it's ready to use!
Wash and lanolise every 3-4 weeks unless soiled.
If you have a heavy wetter, you may need to do 2-3 washes and lanolin treatments before the cover is completely effective.