....and like mentioned above it looks like you want to make sure you plumb it correct, the filter is held on with an o-ring. If you were to go in, the out port, it would push the filter off and then block the out (wrong) port.

Unfortunately you don't have a straight thru fitting you can look through, but I would say pull one of them off so you can get a look inside the filter housing, and if you see the end of the filter, that is your inlet.

Or you can just crack the hole thing open and get a look at it that way. Then you can inspect the filter also.

So if it were to thread in from the bottom of the housing, the top would be the inlet?

You want the crap filtered to be on the outside of the filter media.

Turns out my filter is definitely not Latham.
Latham rep said Fountain made their own stuff for a few years. Mine is the right color to be made by Fountain.

Looks like I'll be opening this thing up. Thx for the nice clear pic.

Took my filter housing apart and discovered both ends are threaded on. Guess they had to be a little different to avoid any patent issues. The end with the mounting bolts is indeed the outlet.