Usually sloppy means messy or untidy. In this use, it means someone who drinks to excess and exhibits very drunk behaviours like slurring their speech, using bad language, spilling their drinks (on themselves and others), not being able to walk properly but instead in a drunk stagger - like many of the characters when they drink too much in K-dramas! haha

Hi Miyeon I haven't read this book, but I understand "sloppy drunk" to mean that someone had gotten so drunk that they had left a big mess behind them (knocked drinks over, perhaps vomited). Normally sloppy drunk would refer to someone being so drunk that they slur their words and stumble around, but because this sentence suggests that you can't see the person in question (Votto or someone), it then makes me imagine the mess that a very drunk person would leave behind. Hope this helps!

sloppy drinking = too much drinking in an unsophisticated way.

Miyeon ~ Some drunks are very neat and hide their tracks, removing bottles from the house, cleaning everything up, leaving no trace of their behavior or activities. Others "let it all hang out" and stagger about, breaking things, leaving bottles in their wake, dishes undone, bathrooms a mess, etc., so this sentence means the drinker was leaving everything visible in the wake of their "fair amount" of drinking.

"sloppy drinking" refers to someone who is unable to govern himself/herself while drunk, engaging in unruly behavior and acting in an undignified manner - starting fights; drunken behavior; sickness; talking loudly; annoying other people, etc.