mechanical engineer /mohammed

Congratulation. You've designed it on a "Rule of Thumb".

so the broplem is how to make sure that the gas pumps can suck the gas from the tank and delivery

Now very simple 2 Rules:

1. If you used your thumb - suck yours .

2 . If you used somebody elses' - suck his.

If you can suck & blow till your face gets red then believe me it might work.

More information is needed:

1. A sketch showing elevations/heights and distances would help immensely.
2. Design conditions of gas pumps is required. NPSHr especially.
3. Flowrates. I assume just standard automobile gas.
4. Size of piping and number of fittings.