I have not been able to find any official rules on how to do this. I want to increase the save DC on some of the items like ghost retch flask, which has a pitiful 12. Does anybody know of some good home-brew rules I could use?
Eh I don't think there is anything remotely official.
I think there are some slight stuff for poisons in the alchemical manuel..
as for house rules I don't really know any good ones off hand.. but I have heard of someone allowing you to add 5 to the DC to make to add 1 to the DC of the item.