Thank you for your review and feedback. The rubber insert is designed to fit tightly once installed so it can create a secure seal in the barrel opening, though it can sometimes be stubborn to install. During installation, it can help to slightly compress or squeeze the fitting and carefully work it into place using a flat-head screwdriver or similar tool. Unfortunately depending on the climate your rain barrel has been in, the leftover glue can also make it tricky. We're glad it sounds like you were able to make it work in the end! Please reach out to our customer service if you need any guidance.