My secondhand 1000ltr IBC tank had contained a softner for plastics.
I gave lots of fills with fairy and water but it would not get rid of the grease on the inside.
I found that my submersible pump was bigger then the hole in the middle so i cut another hole in the top, I will post a pic later today.
I bought some Chic degreaser, put that in with boiling hot water and I could now reach every bit of plastic inside,so I donned my marigold gloves and gave a right good scrubbing.
Used lots of clean water to rinse and their was no more grease.
Hope it helps Neil.