I've just fitted a new basin waste with a plug in a chain. I've tried with the supplied washers etc, and with plumber mait, and have the same results each time. The seal holds whilst the plug is in, however if I run water without the plug in or when I release a basin full of water, I get a significant leak coming out directly under the sink.
The waste has a hole either side for the overflow (seems fairly standard?) and I have lined this up with the overflow at the back of the sink, but it seems that when I release water down the plughole, it is coming out of these overflow holes and then travelling down the outside of the waste.
Despite watching many YouTube tutorials, I can't figure out what I'm doing wrong!