I empty my large guttervac during and after each job at the property I'm working on with the owners permision. It's either put on boarders, under bushes/trees, on compost heaps or baged up for the owner to get rid of. I have even to been know to empty the vac on common land in hedgerows as is just organic waste so is not detrimental to the enviroment or aminals. If there is alot of water in the drum I get rid of that first down a storm drain. I also use ramps instead of trying to lift it in and out of the van and on some awkward access jobs split the guttervac down by taking head off drum, drum of the base and carry the parts seperatly if need be like up/down steps, through narrow gaps etc.
Regarding using a smaller vac there are other posts going on about using a nilfisk 30t that I have seen recently on here.