Be Cool Rad Install

[69CamaroRacer]

While installing a Be Cool Radiator that I bought from a buddy I noticed a red oily substance inside the radiator where the botom hose connects. It looks to be Trans Fluid what can I use to flush this Rad out? Mineral spirits??? THis sucks because I have the car all taken apart and was about to install the new rad.

[Steve68]

anything that will break it down and wash it out, acetone, brake cleaner, etc...