Some racers ran the water overflow from the heads either through the zoomies or to a catch can. Yours just happen to use a surplus(cheap) canteen
There's no line running to it, so it's not being used as a catch can. And if they WERE using it as a catch can, would it be located there? Why would they plumb lines there, rather than run the can up front near the engine? -Brad
You mount the puke can behind the rear wheels in case it overflows. Then the problem is behind the tires and out of your face too. Not sure what the canteen is for, no plumbing so its not overflow. Not big enough to be a ballast box. Maybe its a dikfer.