Waste tank drainage

Stationmaster

Not the most inspiring of topics, but my Autocruise Starquest has 22mm drain hose coming out of the waste tank and ending in a tap.  All more recent motorhomes seem to have 28mm hose.  I can't seem to find replacement taps that will fit 22mm hose anywhere. 
Does anyone hjave an idea how to link 22 and 28mm hoses so that they're watertight? Or a source of suitable 22mm lightweight taps?