With this trick you will get 6+ items and 100 XP from every 10th Pokéstop as long as you keep spinning a chain of unique Pokestops. You will also get an egg if you have an empty slot available.
I happened to notice that the same Pòkestop on my farming loop would usually, but not always give me 6 or more items. At first, I thought it was the Pokéstop itself, but after spinning it 12 times during lunch, it gave me 3-4 items each time.
I have, however, Found out that every 10th Pokéstop spun will give you 6+ items, 100 XP and an egg (if space permits), but you have to follow a specific pattern. Basically, if you continue to spin unique Pokéstops, every 10th stop will give you the bonus. I have detailed below how to do this, but it definitely needs more testing.
My farming loop consists of 41 Pokestops. I would start at the same Pokéstop and repeat the loop 2-3 times. When I discovered the pattern I started testing. For brevity, I will refer to stops as S1, S2, etc and spins as H1, H2.
My regular loop would be Pokestops S1-S41 and 2 loops would give me spins H1-H82. Regular item drop is 3-4 items and 50 XP.
Test 1: Loop S1-S41, 2 rounds. H10, H20, H30, H40 = 6+ items. H42-H82 = 3-4 items.
Test 2: Loop S1-49. H50 was on S1 to start the loop again. Same results as above with all of the spins on the second round giving 3-4 items.
Test 3: Loop S1-S63. H10, H20, H30, H40, H50, H60 = 6+ items. H61-H83 = 3-4 items
It appears that once you return to a previously spun Pokestop, the chain is broken and you lose the “10th Pokestop spin bonus”. I was able to repeat Test 1 with success at 7AM, 12PM and 5PM (before and after work and lunchtime). This meant that 5 hours was enough to reset the chain on the same loop. The next test was to see what the minimum reset time was and the effects from deviating from a unique set of Pokestops. I used a loop of only ten stops, S1-S10.