Couple of points on the vent. Some of the fittings screwed into the housing, some were pressed in. Either can be a bear to remove. The cap can be removed with a little prying without removing the fitting. Once things are clean the cap can be crimped back on with pliers. But not too tight, it needs to rattle around to help with the self cleaning aspect.
One truck I had (can't recall which one) had a barbed fitting with a hose that went up into a clean cross member of the bed. Make a loop out of tubing that fastens to the rail to keep the water out.
