Yes, put a lid on to let it brew - it will smell awful! Good stuff as a feed, though.

I made some (two years running) from Comfrey Tuberosum and kept it covered for 3 weeks but it did not smell. I used a lot on Clematis Josephine but it didn't do her any good - see my latest question.
Perhaps it needs to be the more common one C.Officinale?

Thankyou Spritz and Linmar. I don't know what type of comfrey it is so I'll just give it a go and see if it is suitably smelly.

I found some comfrey plants growing along the edge of a field and dug one up, root and all. I divided up the root into 8 small pieces and now - after 2 years, have 8 plants. I make the smelliest comfrey tea and have used it in poultices too.

What a lucky find. I didn't realise that poultices could be made out of comfrey and by 'comfrey tea' I guess that you mean fertiliser. Haha