Is this normal

I get the same

 

Normal mate, you should see mine.

I've now waxed and sealed my exhaust

 

Yeah it's normal.

Condensation forms inside the exhaust which is then blown out when you next start up, creating the dirty water marks.

 

yep. this is bladddy annoying and i've only had mine for a week!
I tend to keep a rag in the boot just to continually wipe this away

 

Well, longer tail pipes would possibly stop most of it, if your itching to spend money.

 

Try having a white one!

It reminds me of those small white dogs that have brown stains on their fur around their rear end.

On top of that the amount of black particulates that end up on the boot even after one drive is ridiculous.

 

Fit a decat, that stops it.