For sampling from the oil tank, the samples shall be taken from the most  polluted oil tank bottom of the oil tank or oil tank lorry. The oil stored in the oil sampling tube shall be removed, then the sampling can be started. Because the adhesive on the valve catheter at the bottom of the tank lorry may make part of oil be polluted, especially the different oil lorries load with different oil products are more likely to occur the above mentioned pollutants, if necessary, the samples at upper part of the oil lorry shall be taken.