Gasket/O-ring kitchen sink waste trap

[PhiilyG]

My parents have a leak from kitchen sink. My dad removed waste trap and since refitted it leaks, but there wasn’t any kind of seal on it, I got a rubber/plastic gasket that seems
To fit the trap but with it, I can’t get it to screw and lock back on (has lugs so locks after quarter turn. But think waste pipe maybe clogged so would that be causing the leak as the water fills top of trap and just leaks out or is it because there isn’t any seal? My dad swears there wasn’t any seal.

 

[Lou]

Did you manage to solve this issue? If so please tell us how which will help future members