Rack-crack

The cleft between the jugs of an amply blessed, top heavy, well-made woman.

Man - "Here love, hold me pint while I nip t'bogs"
Wife - "You wot, can't you see I've got me hands full here. Tell yer wot, just pop it in me rack-crack
Man - "Alreet love, well I'll be quick then, I don't want me beer getting warm"