As SLF, I can confirm this issue also exists in the passenger compartment on smaller Airbus models, too, like A320. I have experience this myself on several UA flights. Not a pleasant experience. Have not noticed it on A340 or A380, and never on any Boeing aircraft.
The lower recirculation fans on 747-400 deliver directly to the fligjt deck. I have seen and smelt whem a rupture vac waste line aft of the lower recirc fan was delivering a lovely odour straight to the flight deck. As for A330 I have not seen or heard of this. I would be inclined to demand having the toilet extraction filter changed and the toilet waste gate and attached plumbing inspected and leak checked. Also note if its only directly after flushing or a consistant smell..... I have tickets on both of those types.
I'm a boeing man myself. The 747-400 has 2 Lav/galley extraction fans with one running at any time to remove toilet and galley odours. If both fail its a no go. The A320 has a single Lav/galley extraction fan. What the A330 has I don't know but I would expect it to have something similar.
When the smells come into the flight deck they seem to be coming from the avionics compartment. The eyeball vent fresh air is not smelly and is a life saver at the time. I dont think the smells come through the door. So the airconditioning system must be circulating the smell from the extraction fan into the avionics bay somehow?? I plan to write it up each time until it stops. (Still too naive.)
A good maintenance practice to clean the toilets pipes and the smell is to get a bucket of crashed ice (7-10 mm diameter ) and about 10 litres of vinegar and flush it down the toilet. then service the waste tank. its a good idea to check the pipe work near the toilet as well.
I work for an Australian airline that flies A330-2/300. We have experienced this issue and found air flows fwd from fwd lav into flight deck behind sidewall due to airflow issues. This is due to a restriction to the Lav vent extraction system. We have had the restrictor in the fwd lav extraction duct removed and this seems to solve the problem as there is now a greater airflow into extraction system with restrictor removed. Air is thus no longer moving fwd into flt deck but upwards into lav vent system. Our reports go back as far as 2003 and Airbus are aware of the issue.