Confusion regarding unloading instructions

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I have a question for the experienced professionals in this field. I hope all my friends from HaiChuan can help to resolve this issue. The question is as follows: When the liquid-phase discharge interface of the tank truck is connected to the discharge pipeline of the storage tank, and the gas-phase balance pipe is also connected (to maintain equal gas pressures in the storage tank and the tank truck), the liquid inside the tank truck will flow into the discharge pipeline due to its own weight. However, issue 1: After the liquid reaches halfway along the feed pipeline shown in Figure 1, it stops rising further; yet liquid appears when the pressure gauge interface behind the pump in the discharge pipeline is opened. What is the reason for this? Question 2: I separately opened the pressure gauge port to release air in order to increase the liquid level in pipeline 1, but the liquid level in pipeline 1 still did not rise. If Line 1 is not filled, and the fork-type level gauge at position LT59.61, as shown in the diagram, is not activated, the pump cannot be started (due to the low-level interlock protection). My proposed solutions are as follows: 1. Lower the position of the insertion tube of the fork-type level gauge into the pipeline; as a possible consequence, the liquid level before the magnetic pump will not be sufficient, and a large amount of gas will enter the pump, which could damage it. 2. Install a return pipe and a manual valve at position HV59.16, as shown in the diagram, so that the liquid level in the pipeline behind the pump can be used to fill the pipeline ahead. I would appreciate it if those with experience in unloading liquids from storage tanks could share their insights. Thank you all