C260 aha another guessing game What's its name?.
No prizes for guessing right!
Don't know but assuming you are referring to a Thetford C260 toilet. Non I know of in Thetford range have adjustable flush.
Contact www.thetford-europe.com
meantime if the jet is long enough try fitting a piece of clear plastic pipe on it with end cut at angle to cause down flow of flush. You may also find there is angle adjustment on the flush spout.
Download the repair pdf.
on the home page click Service, service information, cassette toilets, repair instructions and download the pdf it covers all models. Use the c250 as much is the same as you go through it also refers 260 on some parts, probably on a design change.
bob uk, August 2014