i'm not sure about mixing comfrey with another leafy plant to have a good fertilizer. I haven't tried.
No need for a vent. I just cut the leaves in pieces to activate the process, fill the bucket (not metal) with leaves, add water (no tap water if you can) cover the bucket, stir every 2 days. when there's no bubbles, the fermentation is finished and your tea is ready. (it doesn't smell very good but you may come to like it when you see the results on your plants)
the exact recipe is : 1 kg of fresh leaves for 10 litres of filtered water. when brewed, filter the mixture (just take a big spoon to remove what's left of stems). then for each litre of tea obtained, add 10 litres of water and water the plants with this fertilizer. I usually add 15 litres of water because i'm always generous with the amount of leaves in the bucket.
the stems that are left in your bucket can be added in your compost bin.
I like the nettle tea because it's "multitask". if you only brew it for a few days (let's say 2 or 3 at the most in your area as it is warm) you can also use it as a natural pesticide on your plants. if used as a pesticide, you will not dilute it.
if you don't dilute if after the fermentation is finished, you can use it as a week killer. so the nettle tea, depending on how long you let it brew and if you add water or not can be used as a fertilizer, pesticide or weed killer. (i killed 2 tomato plants a few years ago, when i forgot to add water).
If you could cut some nettles (in the woods, forest) as long as you're sure they haven't been sprayed with chemical pesticides, you would have a great fertilizer.
