The linkage assembly 24 includes an elongated rocker arm
31 shown as supported in a spaced relation above the tube T
and held by a pivotal support member including a clamp
portion 32 preferably removably attached to the outlet leg of
the tube, an upstanding rod portion 33 extending above the
clamped portion and a clevis portion 34 with a slot at its upper
end into which the arm 31 is slidably inserted. The arm 31 is
pivotally secured thereto by a pin 35 which extends through an aperture in the arm and the clevis 34.