Monday, August 05, 2013 - 10:18 pm, by: Michael McKellar(Mickmini)
you could always mould a fitting plugged with plasticine into the back of the mould and pump water in to crack the mould. (never do this with compressed air - the water does not compress, so is much safer).Can then be used to get parts out of the mould.
I remember trying out some whizzbang wax that was supposed to be the best ever when i made a new front guard for my motorbike (advantage of working at the suppliers). Damned if i could crack that part out of the mould. Should have used the PVA like you did after all.