Hi all, would any more learned back roomers care to comment on the following course of action please?

I have an Audi TT roaster and after a heavy rain shower last week the drain tub behind the passenger seat was full of water. Apparently it’s a common problem and luckily for me the drain tub didn’t fill completely and overspill into the car. I have managed to siphon off the water with a hose pipe but need to get the drain flowing freely again. The drain tub is only visible with the hood halfway up when the flaps that conceal the winding mechanism are open. I can see the water but due to the winding gear I am unable to get my arm down to scoop out any gunk. I have asked Audi but they want the car for three days to completely strip the inside out to access the drain. I politely declined. Over on the TT users forum an owner put his car on ramps, removed under trays and exhaust heat deflectors to access the drain and managed to clear it from the bottom, but this is beyond me. Another user cautioned about poking wire coat hangers or some such into the drain for fear of ripping the soft plastic drain tube.

Then I read a post from an owner who poured Mr Muscle drain cleaner into his drain tub, let it soak for 5 mins and rinsed with boiling water. He claims this shifted his blockage but there was no further postings on any issues down the line and he hasn’t posted an update.

Looking at Mr Muscle, the ingredients are: sodium hypochlorite (that’ll be bleach then); caustic soda (a strong alkali) and some alkyl amine N-oxides (detergents). The hazard warning symbols are ‘corrosive’, I guess that’s the caustic and ‘may be corrosive to metals’. I am tempted to give it a go. As long as I give it a good flush with plenty of water afterwards I think it should be okay.

Any thoughts?