20L does not stand for 20 liters, at least not here in the US, and since the poster's info says they are from Connecticut...

20 gallon tanks come in 2 different shapes, one that is taller and one that is longer. They can be referred to as 20T and 20L, or a show tank and a breeder tank. The 20L is a reasonable size for most young BPs, although some hatchlings will feel too insecure in an enclosure that big, and it is probably too small for adults.