Hi guys. I have just installed a new concealed cistern and it is leaking from it's outlet ( where the back nut holds the syphon in place). The cistern is made of thick, light, plastic and I wandered if it is ok to remove the syphon and put some plembers mate on the inside of the cistern between the rubber washer and the base of the cistern. Is plumbers mate suitable for plastic? I know that applying plumbers mate on big cwsc is not advisable as it does not react well with that sort of plastic but I do not know about the toilet cistern I have mentioned above. Thanks for your time.