i have a 50L TROLLEY which is quite heavy when full.why would you want to drag a DI around adding extra weight?
much better to purify the water beforehand and use the time in the day for cleaning IMO
DAZMOND
Just thought it would be easier than changing barrels, but obviously you have experience so point taken 
to be fair dazmond isnt experienced with wfp - 3 - 4 months isnt enogh time to be giving advise on this sort of stuff but to be fair to him it was his opinion... just trying to say not all advise is from a well experienced wc with 20 yrs knowledge in wfp bits n bobs...
i personally think the 50 ltr trolley is a waste of time, just as quick to use a 25ltr one and just swap the barrels over ...