Relaly grateful for some help please. Have 2 upstairs toilets and 1 downstairs. Last week, the sink in the en suite (upstairs) was very slow draining (normally really quick) and the bath tub was slowish too (it has been cleared of hairs etc). Then the en suite toilet went into slow drain mode. It fills well but comes upto 1.5 inches from the flange (hold your breath time!) It then slowly (about 3-5 seconds) goes down again. Currently the sink and tub are OK. All other toilets have been fine all the time. I have spent an hour tonight plunging the toilet and no change. I have read lots of posts on this forum that talk about where blockages could be and the issues about venting. Is a slow drain like this because of blockage or because of vents. What to do. Thank you.