On the Airstream support site, go the the 2011 Flying Cloud parts catalog into the plumbing section on page Section IV-37 and get the toilet part number (that will typically be for a pallet of 12 toilets).
Part # 690495-03 is an Aqua Magic V, High Profile used in 28' 27FB, 25FB and 30'
Put the part number or brand name into a search engine and find who made (makes) the toilet and go to their site and look at the measurements.
Aqua Magic V Foot Pedal Flush
Since I do not know the trailer in question, the link above should get the OP into the correct brand to do research.
I was curious about our soon to be built Classic's "facility" and did the procedure above. The enclosed image is the information I found for the Dometic 18" tall toilet used in a Classic and also used in our 2013 25FB International Serenity. Check out the measurements. Camping World had a special on this model Black Friday.
Hope this helps.
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TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell
2014 31' Classic model 30 twin beds, 50 amp service, 800 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels