1 inch should suffice with the amount of water that comes down the spout, insert as a 45 degree angle upwards with a 45 degree cut to catch water with a screen on it ( dont glue the inlet pipes so they can be removed for cleaning, glue everything else ) depending on how much water you need and use for garden as well, the 275 gallon totes are nice as well, in a metal cage you can also store items on top to save space.just use a MUCH larger pipe as inlet. and make sure you have a full diameter clean out at the bottom.