Most modern spray booms tend to have "dead ends" that resist being fully cleaned out when water or cleaning solution is flushed through the system, unless all the pipe end caps are physically removed and then reinstalled. Ontario province agricultural engineer H. Spieser describes the problem (in vol. 11, no.1 of CROP PEST ONTARIO) and notes that, by modifying boom sprayers with quarter turn ball valves, or cam-lock caps, some spray operators have devised quick, easy, and effective means of flush-cleaning.

The information can be found at http://tinyurl.com/pqjsk