This is a great answer, and the picture goes a long way to show how actually simple and straightforward it is to keep the portafilter clean, instead of the widespread fearmongering and dire warnings that abound most everywhere else online! Two Thumbs Up, Henry H!
Going further, lifting the spring shown in the picture will also lift the needle valve on its hinge (don't worry, it won't fall off, just lift the spring and put it aside, it'll slip right back on no problems). This exposes the valve seat for cleaning and it's then just a matter of using a toothbrush, some Q-tips and a household degreaser such as ammonia (caution, it's fairly corrosive, use dishwashing gloves) or glass cleaner to remove the gunk that may have made the mechanism stick in a partially closed position.
When you do that, just be careful not to do it too forcefully, notice on the picture the little feather spring, how it should be set in, should it come off. I simply put my finger on it while I work with the toothbrush so it won't. In any case, it's very easy to put back on but it's a small part to look for should it fly off ;)
Cleaning the outlet spouts in the handle is just as deceptively simple, also remove the handle end cap to clean the inside of the handle, it's hollow and this is where the pressure release goes in case of need, it may be full of coffee residue as well, just imagine what ugly after taste it could give your coffee...
Total actual cleaning time, not counting soaking (I suggest you let it soak an hour in pure household ammonia in a covered container to soften the gunk), was about 30 minutes, including reassembly and running clear water through it from the machine.
Now brew yourself a fresh coffee and taste the best coffee you've had in a long time, possibly not since the machine was new ;)