Personal injury protection or PIP is an insurance that Washington state requires auto insurance to offer to you through your car insurance plan but, you may choose to deny coverage at the time you sign up for your policy. This insurance covers you for bodily injury in the case of an accident regardless of who is at fault. Massage is one of the many treatments that are available to you under this insurance. 

A 3rd party claim is where the at fault person's insurance covers your medical bills due to an automobile accident. You may choose to use a third party pay when you are not at fault, you have retained an attorney and your personal automobile insurance PIP coverage has been exhausted. 

Generally, it is best to have your insurance pay for the medical bills associated with an accident regardless of who was at fault. They are on your side and just want to see you get better. Once you have discontinued treatment, your insurance company will be reimbursed for the expenses due to the accident if the other driver was found to be at fault. You would choose to use the other drivers insurance if you elected not to carry the personal injury protection coverage or you have reached your PIP benefits limit and the other driver was at fault.