Some may recall that I fitted an odour extraction system to our bathroom toilets, to suck air directly from under the seat, using the flush holes in the rim.  The effectiveness of this has just been commented on again, so I thought it worth doing an update.   For those that didn't see the original posts on this (I've a feeling they may well have been on this forum's predecessor, so now lost) I decided to plumb the space above the cistern on each WC to the MVHR extract ducting, using 40