Answer:
I am there when you sit, but gone when you stand. What am I?
I go in dry and come out wet. The longer I stay in the stronger my surroundings get.
I have a name that's not mine and no one cares about me in their prime. People cry at my sight and lie by me all day and night.
As I went over London Bridge I met my sister Jenny; I broke her neck and drank her blood and left her standing empty.
Who is your mother's only sister's son's brother's aunt's daughter's sister's father?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.