@baiteh @darrenhartland @fesshole depends how often monster turds happen? If a small flush uses a (made up) 1/6th of the water of a full flush, but 1 in 4 shits is like King Kong's finger (thanks Inbetweeners) then by doing the ineffective flush first you're using more.
I'm about 99% sure that if the OP reads this, they've probably also kept a spreadsheet of the results and can let me know whether I'm worrying about nothing.
Open question: does one need to send a certain amount of water down the waste pipe (over the course of, say,a month) to flush away the solids and prevent the pipe from getting clogged?
@CppGuy @fesshole absolutely. If it's a shared drain running across some houses, then each house also needs to regularly flush the right amount of water.
Source: house 'below' me on the shared drain was empty for a year. Had sewage coming out the drains on my property as a result - everyone 'upstream' of us had their waste stopping on this empty property