Stock determination

Hi Experts, I need your expert advise on the below scenario. We have a resource which is a container where base oils are produced. So this is called base oil resource. there are pipes called prefiller. There are mapped as resource which are connected from base oil tanks to blending tanks. so i have first operation in the base oil resource and the second in prefillers. the user want to know what is the quantity in the pre fillers pipes after first operation. This may be possible in tank planning but we are not using that. can someone suggest a way to achieve this.? Regards Shruthi