DRealization

import numpy as np

factory_struct = {
    "pipe": [],
    "input": [],
    "pump": [],
    "tank": [5, 6, 7, 8],
    "pipe_c": [],
    "tank_g": [9, 10, 11, 12],
    "stock": [13, 14]
}

L = [(1, 5), (2, 6), (3, 7), (4, 8), (5, 9), (5, 10), (6, 10), (6, 11), (7, 9), (7, 11), (8, 12), (9, 13), (10, 13), (11, 14), (12, 14)]


D = []

for i in range(len(L)):
    if L[i][0] in factory_struct["tank"] or L[i][0] in factory_struct["tank_g"] or L[i][0] in factory_struct["stock"]:
        for j in range(i, len(L)):
            if L[i][1] == L[j][0]:
                D.append((i, j))

for item in D:
    print(item)