We were fortunate in obtaining 3 each 65 gallon used pickle barrels.  We decided that to put these choice barrels to good use we would begin to collect rain water.  But in order to begin the collection we needed to tie the barrels together with PVC schedule 40.  So we purchased galvanize pipe to thread into the barrel, secured the connection with 1 3/4  inch electrical nut.  Then we threaded 1 1/4 inch PVC into the galvanized fitting.  Slip connection on other side to accept 1 1/4 in PVC which would connect into either 90 degree elbows or T.  Because the barrels will be collecting rain water from the house gutter system we connected a quick empty to clear debris coming down the drain pipe.  Also used a 3/4 in bib to connect to a hose.  On the top of the outside barrel is the overflow.  We will connect that to a hose a drain out into the grass.  Need to keep the water away from the house foundation.