smelly drain - fungus type culprit found!

Didn't see your original posting-so someone may already have suggested straightforward household bleach which will certainly destroy the offending growth.

The smell you mention and the fungus is common to many drainage systems but you don't smell it because of the U bend--- water seals. In your case the stinking water is sloshing onto the drain cover. Why not extend the downpipe so it discharges below the water surface in the drain

It would also be worthwhile trying to find out what this fungus is and how it occurs... if its common, there's bound to be a remedy that can prevent it re-appearing. On the other hand, If its never been seen before, you could become famous and make some money charging biologist-types for access to your poo-stack!

If it were me, I'd give it a good flushing with Jeyes fluid (forget the gimmicky branded products) and if that doesn't eradicate it, replacing the pipes wouldn't hurt... they're probably due for it anyway!

good luck.

d.

Isn't this lethal to plastic pipes?

I'd go for chlorine, but the problem is that it won't touch all round the inside of the pipe. A foaming cleaner would be better.