I have moved into a one bedroom council bungalow a year ago. There has been a very strange smell in the bathroom, it isn't there all the time, in fact there isn't any particular pattern of time when it appears, sometimes morning - sometimes evening. This smell is not bad but it's sickening, smells like an undiluted bottle of Tesco's double strenght blackcurrant juice. It isn't coming from the drains or anywhere else I can put my nose. Trust me, I have cleaned and cleaned to no avail. Suggestions welcome - it's driving me crackers!!
Sometimes the wax seal at the bottom of a toilet is no longer effective, which can allow a strange Oder to escape from the drain pipe beneath it. It is simple problem to fix if that is indeed the problem.
Or if your unit shares an exhaust duct/ vent with other units, sometimes negative pressure on the duct will cause exhaust gases to move into your space instead of out of your space. Then an adjustment will need to be made to the vent near the top of it - sorry, I do not how that is actually fixed.