Ron, your querey does seem strange unless you present a few more relevant facts as to what your concern actually is. One very obvious reason for the really basic type of suction unit to be on the wall where the schrader valve is, is because the wall provides a natural reference for the suction jar. In the case of the type using a ball-float mechanism, it has to be up-right otherwise the contents may not be blocked from being sucked back down the pipeline by the valve when the jar becomes too full. If you have an in-line suction unit (which personally I have not come across) then one naturally assumes that it has been constructed to lie or stand-alone or be supported in some way or the blocking mechanism is of a different type not requiring vertical orientation. If this is not the nature of your concern, would you care to elaborate further?
