Read all of this before doing anything.
The front cover must be removed, to get to the macerator/discharge pump area of the head.
When removing the front cover, (round inspection cover with 6 screws holding it on, part # CH18W), use a table knife or something thin to work into the crack between the flange of the front cover and the metal housing. Tap it down (gently) with a hammer, to get it started coming off. Do this in several places around the front cover. It only actually extends inside the metal housing about 1/4", so once you get it started, it should come right off. Don't pry it with a screw driver, or you'll crack it. Then look inside with a flashlight. Have plenty of rags or paper towels handy, because whatever is inside the macerator chamber will come running out onto the deck when you remove the front cover.
What you should see first, is the white "star wheel" cutter blade (CH121), about 2 1/8" in diameter - this is the actual macerator. Looking further in, you'll see a series of "teeth" or slots, all around the outside perimeter of the cavity as you look inside. Next, and this is particularly crucial, you should see a black elastomer washer, immediately behind the teeth I just mentioned. This part is the key to the head pumping out properly. If that part isn't situated correctly, or if it isn't there any longer, or if it's all chewed up - the head won't pump out.
A bit of explanation: the actual discharge impeller, is a centrifugal impeller. Centrifugal = "center" - it draws only from it's center. The purpose of the flexible washer is to direct the flow of waste through the hole in the washer into the center portion of the impeller, where it draws from. If that washer isn't there, or if it isn't sitting just right, the whole face of the impeller will be exposed, and it can't draw any water or sludge. Net result is that the head won't pump out, or if it does, it will be at a very slow rate.
This part will likely need to be replaced. It isn't terribly expensive ($18.28 from Raritan; $12.95 from BoatFix) and it's a good idea to keep a spare on hand at all times. They tend to "go" without any warning - but it only takes about 20 minutes to replace one, once you learn how to do it.
OK, getting back to it, you clean out the area as well as you can, then unscrew the white cutter blade from the threaded hub that it mounts on (counter-clockwise, it's a standard right-hand thread). You'll need a glove or a thick rag, as the edges of the cutter blade are relatively sharp. Note: if it won't "break loose" and the whole motor shaft begins to turn, get a large screw driver and put the blade of the screw driver in one of the cutouts of the cutter blade on the LEFT side. Then rap the shank of the screw driver (down) with a hammer, to get the threads started. Once it has started, you can unscrew it by hand. Set it aside. Now, bend the new black washer (called a Discharge Pump Wall, Raritan part # CH120) in half, like a taco. Tuck it in behind the cast-in slots in the bronze housing. There's a groove cut back there, immediately behind the slots, that the washer must snap into. Work it around with a small screw driver, until it snaps into place. It should sit just about perfectly flat, once it's in position. Then screw the cutter blade back on, just hand-tight and replace the front cover with the "scoop" facing down. If you cracked it when removing it, put it back on anyway - it won't usually leak. Then order a new one (CH18W, $35.68 from Raritan, $25.29 from BoatFix).
The head should now work "good as new."
