I haven't tried this in this situation, but if you Google a product called CT1 it sticks pretty much anything to anything. I would suggest giving them a call for advice on compatability.
Discuss Sticking Pvc to tanking in the Tanking and Wetrooms area at TilersForums.com.
Reply to Sticking Pvc to tanking in the Tanking and Wetrooms area at TilersForums.com