I recently was making a 325 gallon watering system for deer in front of my game camera. This adapter is specific to the IBC tote I have. I'm willing to adapt for others, but you have to have specific specifications, TPI/diameter, etc. -- send me a message on here and I will upload as soon as I can. This worked great for me to get it down to a garden hose and then to watering system. The same could easily be done for rain collection or anything that uses an IBC tote. When trying to keep it cheap you can easily use a cut piece of garden hose with adapted ends. I printed in ABS to help with standing up to the UV exposure. It has worked well for the last 6 months. Since it was a gravity fed system, no rubber grommet was required- water tight by design.

Dimensions as I recall (sorry it was from 6 months ago), was 82 or 83mm with a tolerance of 1mm, so that it will screw on easily. Again, it was water tight even with this tolerance being so large. I had a little bit of stranding without support, but overall did well.

I'm always happy to post stuff for free. For those that have asked, feel free to support me on Paypal (paypal.me/APC84), I'm happy to post more free stuff and take suggestions.