I'm currently running an Onkyo 805 and will be using four identical 12inch subs, my question is how to properly wire all of them to my receiver.

Subwoofer pre-out, Y-splitter to Y-splitter + Y-splitter

Some options will depend on the sub. I am assuming these are all powered subs. If your AVR only has one sub out (most likely), get 3 1m/2f Y splitters. Plug one into the AVR's sub/lfe out. Then plug each of the remaining 2 into the two connectors on the first splitter. Now you can run sub cables from each of the four connectors to the individual subs. If the subs have nonfiltered line outs, you can daisy chain them.

There are all sorts of places you can put the Y-splits, too. For example, depending upon where the subs are, it may be most convenient to put one split right at the receiver and run 2 separate RCA cables, one of which goes to one pair of subs and the other to the other pair, with the second split being done at the other end of the cable. Etc., etc.. In other words, you can do what works best, practically and aesthetically, for your layout. You can also daisy chain by plugging a Y-adapter directly into the back of a sub, at its input, and then running a cable directly from there, from the other arm of the Y, on to another sub.

Male to 2 female and female to 2 male Y adapters are both available although I think one is more common and easier to find than the other. But there are also male to female and female to male converters/adapters that can convert the ends of Y adapters into anything you need and they are available very inexpensively. Point being, you don't have to let the type of Y adapter you are able to get your hands on, and the particular ends it is equipped with, dictate your wiring scheme.