I have an old Paterson colour print developing drum for 8x10". I have no other instructions than solution volumes printed on the side of the drum (90ml).

The lid has kind of a cup where poured solution stands until the drum is placed on it's side, when the solution spills in the drum.

The problem: There's small gaps on the lid's threads and developing solutions keep leaking thru them. But what is the purpose of those (see attachment image, it's upper right part). I can't figure the reason for them as the lid has already usual draining hole.