It means the men would indulge in such excessive drinking that they would consume all the alcohol in the house.
unconscionable: greatly exceeding bounds of reason or moderation. toping: drinking excessive amounts of alcohol. fairly: pretty much. drinking the house dry: drink all the alcohol so the house is dry, like a well.
The Three Strangers by Thomas Hardy
Shepherd Fennel had married well, his wife being a dairyman's daughter from a vale at a distance, who brought fifty guineas in her pocket--and kept them there, till they should be required for ministering to the needs of a coming family. This frugal woman had been somewhat exercised as to the character that should be given to the gathering. A sit-still party had its advantages; but an undisturbed position of ease in chairs and settles was apt to lead on the men to such an unconscionable deal of toping that they would sometimes fairly drink the house dry. A dancing-party was the alternative; but this, while avoiding the foregoing objection on the score of good drink, had a counterbalancing disadvantage in the matter of good victuals, the ravenous appetites engendered by the exercise causing immense havoc in the buttery.