go on eBlag and look for gunk engine degreaser its about 10 quid for 5 litres.
rub plenty on chain with a chain cleaning brush wait 5 mins
then wash off with soapy water.
I then I use a little bit of brake cleaner on the chain and let it dry.
then put some wurth dry chain lube on.
Used gunk a lot on engines, quite aggressive, don't think I'd want to use it on O-rings. Use both of the others tho