He's talking about people who make crappy 2 or 3 line posts and then upvote themselves through shill accounts.

I saw a guy post two or three posts a day containing 2 lines of gobbledy gook a day, I mean, it had zero meaning, just a bunch of words. He had enough SP to give himself a $20 upvote for each of those posts.

Steemit works via reward pool, so 64,000 Steem is allocated via the blockchain to Steemit users each day. Our votes decide who gets what percentage of that pool, ergo people like our man that I referenced above is draining that pool with his crappy posts and high SP votes.

I think drainers is probably a better term, it makes more grammatical sense methinks! :-)

Cg