This has happened to us on occasions, Islay, and the cause has always been loose connections between the transparent plastic water pipe and the submersible pump or where the pipe passes through the container cap (upper and lower).
Over time, the plastic becomes stretched and loses its grip on the spigots. If you have sufficient pipe length, you could always cut a centimetre off and reattach the pipe on a fresh, unstretched end.
These are the three connections that I'm referring to:
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You may also need to replace the clips/cable ties.
Hope this helps.