radially extending peripheral groove 136 is provided on valve insert 66 for accommodating conventional o ring 138 therein another o ring 140 is disposed around projection 106 when the adapter assembly d is mounted within nipple 16 o ring 140 seals opening 142 in flush valve body 10 through which projection 106 extends and prevents back flow of water from insert 66 to flush chamber 60 likewise o ring 138 substantially seals and prevents back flow of water from recess 110 to chamber 60 as best shown in fig7 leg 130 of passageway 120 is disposed between o rings 138 and 140 as best shown in fig7 valve insert 66 includes larger diameter section 144 and small diameter section 146 preferably the length of smaller diameter section 146 is less than the length of larger diameter section 144 as best shown in fig7 leg 128 of passageway 120 runs the length of smaller diameter section 146 and a portion of the length of larger diameter section 144 the leg 130 of passageway 120 however extends transversely thereto within larger diameter section 144 passageway 112 extends through the length of projection 106 larger diameter section 144 and the smaller diameter section 146 but short of recess 110 further leg 130 of passageway 120 is disposed adjacent projection 106 and away from recess 110 as best shown in fig3 clearance 148 between nipple 16 and valve insert 66 is provided due to clearance 148 it is not necessary that side opening 124 of l shaped passageway 120 be aligned with base chamber 126 when the adapter assembly d is installed in nipple 16 since when flush valve a is activated described below in detail water from recess 110 will make its way to base chamber 126 through clearance.