DONE!! Wow that was fast Answer Tank-5 Explanation: This is a variation of Which Tank Will Fill First Brain Teaser but in this puzzle connection between tank-5 and tank-2 is closed so water will go into tank-5 from tank-1 but not go to tank-2. Therefore tank-5 will be filled first. Remember the rules good luck guys :) First 5 that gets its right gets tips #Giveaways