And two things I learned in the military.....
1.Never upset the pay staff or the cook.
2.If you want to be totally invisible, walk around with a pen and note pad in hand while appearing to "check" things :-)

I don't think 2 advisable - you might get redirected to another task (own experience). A really foolproof method is recommended by my friend Don Pedro (a real Ph.D., oriental languages), Pte, retd: Dip your hand into the waste oil barrel and grab a spanner. No superior will think of giving you additional orders - you are too dirty for the job.