Question:THE GEMARA BRINGS A BERAISA TOWARDS THE TOP OF 20B.THE BERAISA STATES THAT A PERSON MAY NOT HOLD THE WATER FOR THE ANIMAL WHILE HE DRINKS RATHER HE MUST PUT IT DOWN AND ALLOW THE ANIMAL TO DRINK ON ITS OWN.ABAYEI SAYS THAT THIS BERAISA IS SPEAKING WHERE THE TROUGH IS A RESUS HAYACHID ITSELF,AND PART OF IT IS INSIDE THE PASSIM AND PART IN THE RESHUS HARABIM.THE REASON YOU CAN NOT HOLD THE BUCKET IS BECAUSE OF A RABBINIC DECREE LEST YOU COME TO FIX A BREACH IN THE AREA OF THE TROUGH WHICH IS IN THE RESHUS HARABIM THEREBY TRANSFERING THE BUCKET WITH INTENT FROM THE FLOOR OF THE RESHUS HARABIM BACK ONTO THE RESHUS HAYACHID.MY QUESTION IS "ATU BIRISHII OSKINUN?" IN ORDER TO FIX THE BREACH YOU WOULD HAVE TO TRANSGRESS AN ISUR SHABBOS(MACEH B'POTISH OR AT LEAST M'SOCAIN).
DO WE GO OUT OUR WAY TO MAKE A G'ZEIRAH FOR A TRANSGRESSER?
RASHI (DH Dilma) explains that he will forget that it is Shabbos and carry out into Reshus ha'Rabim. That is, there is no fear that he will actually fix the breach in the trough. Since it takes considerable effort to fix it, he will certainly remember that it is Shabbos before he fixes it (we find similar reasoning to this in Tosfos 40a, DH Ha). However, we fear that he will carry the bucket out to Reshus ha'Rabim before he remembers that it is Shabbos.
(TOSFOS explains that he goes into Reshus ha'Rabim only to see if the trough needs fixing and how to fix it, but he does not go to actually fix it. This certainly answers your question. (Tosfos gives another explanation as well, see Insights to 20b).