[xj-s] Funny vent tube behind battery?

This weekend, while cleaning out the dust and debris that collected below my
battery, I noted for the first time a rigid black plastic tube that starts
behind the fuel tank bolted rear bulkhead, drops down along the right side
of the bulkhead, then zigs horizontally to the left behind the battery, then
zigs down, across to the right again, and down again, ending up open end
pointing down somewhat below the battery but nowhere near the grommeted hole
in the trunk floor below the battery. I can’t figure out what this tube is
is; if it’s a battery vent, the top part isn’t near where the battery vent
would be and the bottom part doesn’t vent out of the car; if it’s some kind
of fuel tank vent, again I’d expect it to exit the car, and I’m concerned
that it doesn’t. If it’s connected to the ECU, isn’t it in the wrong place?
Does the ECU lurk behind the bolted fuel tank bulkhead?

Anyone know what this thing is?

'92 XJS convertible 32k