The verb 'To Waz' in northern English dialect means to urinate.
In both West Yorkshire and East Lancashire, offal was very popular and when produced en masse the offal was cooked in linens resembling large pillows and were referred to as 'socks'. These prevented the offal from burning and being ruined when coming in to direct contact with the base or sides of its cooking vessel.
Unsurprisingly these linens absorbed the odour of the offal (which is similar to urine) and were discarded. They were colloquially referred to as 'Waz Socks'. The derogatory sense of a 'Wazzock' to this day refers to someone discarded of having any point, purpose or worth.