Hi guys. Thanks for the info so far. I think I better go back tonight
as I have a couple of things to try. I will try the caustic soda. It
does say to "leave for 30 minutes" and use cold water. Add soda to the
water and not the other way round. Is the leaving for 30 mins
necessary?

Secondly what type of detergent should i add to the boiling water? Will
normal washing up powder do the trick or should I use something else?

Many thanks everyone.