You wrote,
"I did try leaving a bit of water in both the sink and tub last night to see if the smell was meybe due to a faulty s trap but the smell was still there this morning."
Sorryto have to tell you this but you're going to have to test the tub, lavatory and the shower, (if you have one) again.
You forgot to block off the overflows so the smell could bypass the water in the fixture drain and come right out the open overflows. As you can see I'm fixing on the traps because a low water seal level in a trap would give you the problem you discribe.
Let's test those traps again. This time put duct tape over the overflows when you put water in the tub and lavatory. And if you have a shower close off that drain and run water in it also. Do this before you go to bed and give it the sniff test in the morning.
A trap loses its seal in two ways. The most common is a blocked vent. If a vent's blocked the water draining down a drain pipe will put a vacume on the trap. The resulting suction can draw the water seal down far enough for sewer gas to escape. The other is when a metal trap corrodes away at the bottom letting water seep out and sewer gas to get out into the air.
Before any kind of repair can be effective you must localize the problem. Once you pin-point the source the repair can then be started and not before.
Tonight, test the traps and get back to me tomorrow morning. As for industrial cleaners, click on.
http://search.msn.com/results.aspx?F...strial+cleaner Good luck, Tom