Try a beach-block in the cystern?
If the gas bubbles up through bleach each time then it may filter out some of the smell.

If you can't get it fixed properly, of course.
( Ugi , it's a game of give and cake, Fri 14 Sep 2012, 10:36, 1 reply)

I don't have access to the cistern.
The plumbing in this place is interesting. They pump desalinated water into a vault under the building, which is then pumped to a tank on the roof and gravity feeds to the apartments. Each bathroom has its own tank type water heater hanging up near the ceiling. During the summer if you want hot water you turn on the cold tap to take it from the roof, and for cold water you use the hot tap to take it from the tank in your air conditioned apartment.

I think I have it resolved. I took the lid off of the tank and adjusted the float to fill it with more water, to flush it more thoroughly. That seems to have been effective- I did it a few days back and the stench has gone. Who knew that an exorcism only needed a bit of extra water and some liquid bleach?
( The Resident Loon Not a demographic. Do not measure., Sat 15 Sep 2012, 6:59, closed)