a trailer question.

[drivin_me_nuts]

I noticed a trailer today that I haven't seen before. It was carrying a container but what struck me as unusual was that at the rear of if was a value similar in dimension to those on grain trailers and suchlike. also, there were cylindrical tubes running the length of the trailer, just below the load bed, one each side I presume.

can anyone tell me why this trailer would have such a valve on the back of it and what the cylindrical tubes are for.

cheers.