Hi all, thanks skiberger for the advice, I'll try the test spot of plastic. Now for a plumbing question: I have all the rough for the bathroom in but the only drain vented is for the sink. Does that mean the toilet and shower will vent through that on OK or do they need to have a vent as well?

Snowak, if you can post this question in the plumbing section, Tom (speedball) can give you a proper answer.