theres a fine art to this mate...wot i do is fill a wet bucket and 2 mixin buckets 1/2 full..knock up, lay on
scrape any waste into an empty bag where is goes hard, tip wet bucket into mixin bucket, wash out and tip back into wet bucket
flatten off and knock up topping, repeat..
trowels + hawks get cleaned in the wet bucket, and i dont use a spot...
all the slop sinks to the bottom of the wet bucket...
finish the set, dig a small hole behind the rosebush agitate wet bucket and tip into hole...
repeat for next set
in absence of a handy rose garden/bit of loose earth you can just about get away with gently tipping the top clearish water down the drain and scrape the slops into a bag (bin bag helps) it all sets anyway before you set off home...