Bristol 603 - compartment drainage

[Peter Hoskin]

A recent 2 hour trip in heavy rain resulted in a wet carpet in the boot, mainly on the near side. It would appear the water was coming down rather than up. Removal of the carpets etc. should 2 pipes clipped to the wing which exit behind the rear wheel with one only on the offside. I assumed one came from the petrol filler compartment and the other from the cabin air exhaust space. Previously I had noticed drainage from the petrol filler comp. dripping from under the rear wing but on this occasion I find the drain to be blocked so I need to explore further. Removal of the grill of the cabin air exhaust space revealed no drain from that space, surprising because a car wash or enthusiastic use of a hose must lead to water entering this space.
So what is the purpose of the second drain pipe? I thought it might be an air release from the top of the fuel tank but there is no such fitting so what is the purpose of these drain pipes, one each side of the rear wheel? A search wire went a long way up it.