I am re-doing my kitchen and have fitted a new sink. It is a 1.5 size sink, neither sink has an overflow spout. When the plug is in one sink if you pull the plug out the other sink it wont drain (because their is no air behind it I assume) and leaks from the drainer unit under the sink. The drainer unit probably just needs tightening but is it odd that their is no overflow, should I cut one out?