Yeh it's always different because I do it for different amounts of time each time. Usually in the region of 4-500k each time. Sometimes less if I cba to sit there for half an hour, but never more than that due to risk of crashing and wasting my time.
As for the per tap question, I think it's irrelevant because if you spend that time getting up to ~$1200 a tap then any increases from visiting other towns along the process of collecting seems insignificant (+$2/3 here and there) so if I start on $1200 it will end on maybe $1300 or so.
