Results are all over the map. I've seen as much as two pounds per five gallons down to as little as five grams per five gallons. Tamarind can be found in its natural form, semi-processed blocks with the exterior skin removed, paste/concentrate and syrup. I'd imagine in looking at recipes that the smaller the volume of tamarind the more processed the tamarind product that was used. You have to be careful when using any kind of processed tamarind product as many contain sodium as a preservative.
The easiest way to use unprocessed tamarind is to soak it in hot water (some will boil it) so the fruit inside the pods will dissolve into the water and then you use the water. That is a lot easier than trying to remove the pod skin, seeds and veins or alternatively trying to remove the pod skin and then scrape off the fruit. For brewing that would make the easiest approach just removing the pod skin and chucking the whole thing in your mash and let it steep. You'll lose some of the aromatics through the boil but tamarind is often used in food where it is cooked anyway so it might not be too damaging to the tamarind character.