We are using 1.2.2 stable snapshot 502, apologies if this is fixed. The drain does not recognize that xp has been used by player. Eg. If player has 30 levels and does a lvl 30 enchant and then steps onto drain the xp resets to 30 and drains into tank. This also occurs for multiple enchants, not just the last enchant done. The tinkers construct XP storage table (removed from mod) had the same issue.

Thank you for the bug report, We'll look in to this.