Manky Expansion tank

[Roylewaa]

I grabbed an expansion tank at the scrapyard this morning for a few quid, anyways its stained brown and fairly manky inside, ive had it soaked in bleach and hot water for a few hours which has cleared about 60% of the poo out

Is their any tips or tricks to clean out the poo further, I was thinking about powerwashing it out at my local garage

Or am I wasting my time and being a cheapskate and should just go and buy a new one?