For me and future builders who end up with coolant adapters that are tight fitting (both on the hard side pipes and the corrugated piping), post your tricks to get them installed.

For most of mine, I've used a vise to install the adapters onto the corrugated pipe. Gently clamp the pipe into the vise, use some pliers to pre-stretch the adapters slightly, and with some silicone based grease, they go on with some patience.

Obviously, this doesn't work in some places or if the pipe ever needs to be serviced.