In just eight short lines, the speaker imagines something grim: finding their own heart floating in a toilet, discarded like waste. The word "expect" matters here. The speaker isn't afraid of this or hoping against it. They talk about it flatly, as if it's simply the next thing on the schedule.
The heart is usually a symbol of love and feeling, so calling it "dirty, useless junk" that the body "doesn't need" is a bitter twist. The poem suggests someone who has been hurt, or worn down, and who has started to see their own emotions as a burden. Judging by the tone, they may feel that caring too much has gotten them nowhere, and that the body would be better off without it.
The mood is cold, blunt and a little darkly funny. The plain language and the ordinary, unpleasant image of a toilet make the sadness feel more real, not less. There's no drama, just quiet resignation.