Kitchen sink philosophy is a humorous reference to an "all-in, all-inclusive" approach to a task that indiscriminately incorporates a lot of junk along with whatever jems that it might also include.
It is a play on the stock phrase "everything but the kitchen sink." This phrase is a derogatory reference to situations in which "everything" is indiscriminately included with a plan, a project, an idea, a piece of legislation, etc. with little or no regard to the practical or aesthetic consequences of the resulting clutter or mess.
The kitchen sink as a metaphor can be taken in two ways: 1) iconically, as a hodgepodge pile of "dirty" dishes, or 2) conceptually, as repository connected to a "drain" that is under normal conditions specifically designated for unwanted and/or leftover rubbish, slop, filth and waste.
The most common play on this stock phrase is to say something like: "They put everything in there including the kitchen sink."