E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
in drinking bumpers, means that the wine-glass is not full to the brim; between the wine and the rim of the wine-glass light may be seen. Toast-masters used to cry out, Gentlemen, no daylights nor heeltapsthe heeltap being a little wine left at the bottom of the glass. The glass must be filled to the brim, and every drop of it must be drunk.