s = {
    "-HVC1": [
        (0,8),
        (12,18)
    ],
    "-HVC2": [(9, 17)]
}

seq = []
with open("my_huge_file.txt") as file:
    for line in file:
        if line.startswith("-"):
            tx = line.split("tank", 1)[0].strip()
        else:
            for start, end in s[tx]:
                seq.append(line[start:end])

print(seq)