I made the following addition to storing the hose under the frame of the motorhome.  Now nothing is visible from the outside of the GMC and all of the dump operation is under the Onan door.  The plastic (sch40) conduit routs the Macerator hose down beside the Onan and then along the bottom of the frame towards the front of the GMC.   Pictures below.

http://www.gmcmhphotos.com/photos/showgallery.php?cat=3060
gene

What is the radius of the 90 deg pieces in the s tube?
It is standard plastic (sch40) 1 1/2 inch electrical conduit and the 90s were long sweeping.    I think because conduit is made to pull wires through, so the joints have no lips and the curves are long and sweeping.

What is the OD of the hose?
I am not sure but it is a good quality heavy duty 3/4 inch garden hose.  Use one with a hard surface so that it will slide easly.

Is the 2" electrical conduit made of metal or plastic.  Metal would take more abuse down below the coach.
I used the plastic, I thought it was lighter and I might have to bend it, I did not have to bend it.

Did you cap the front end of the conduit?
No I left it open for it to drain from driving water and any drips.  It has been suggested to put a 45 degree on the end to keep the water and road dirt out of the pipe.

 Drain holes there?
Yep several holes down the length of the pipe

I assume the end of the hose is just cut off; no fitting.
I kept the hose end on.  I put a brass cap on the end when I am through dumping.  It is smooth and slides easily and stops any drips.

And the hose really does slide easily thru the s tube and all the way in?
Yes it seems to go in very well. DO NOT WAX THE HOSE.  I tried this and it made the hose stick.  I removed the wax and used a silicone spray. It now works well but tries to grab at the corners.  I will see how it goes in the future.

good luck gene

Y  Connect Left Side  Y Connect Right Side
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                           PARTS LIST

MACERATOR PUMP          MODEL 18590-0000         JABSCO (12v)      1 ea          $165
3" GATE VALVE                   T-1003VP                           VALTERRA          1 ea           $ 13
3" MALE ADAPTER             T-1005                                 VALTERRA          1ea             $3
3" FEMALE ADAPTER                                                      VALTERRA          1 ea            $3
3" X 11/2" ECCENTRIC        1041-1                                 VALTERRA          1 ea            $4
CPLR (slip to thread) 1 1/2"   5803-2                                  HOME DEPOT    1 ea            $1
RUBBER 3" TEE (313 x3)     PQT-300                              HOME DEPOT    1 ea            $8
1" WASHER HOSE                 Dish Washer                        ACE HWD.            l6ft            $ 20
20 amp CKT BKR                    AUTO PARTS                                                    1 ea            $5
20 amp SWITCH                       TOGGLE (on/of!)               AUTO PARTS      1 ea            $5
10 AWG WIRE                         AUTO PARTS                                                    1 ea            $5
BRACKET, MOUNTING         CUSTOM                            MISCEL                1 ea
CLAMPS                                     MISCEL                                                             as reqd
PULL HANDLE ROD               1/4" ROD                              MISC                   2 ft            $3
1/4" to 1/4" COUPLER                                                           ACE HWD            1 ea          $1
STOW TUBE                               1 1/2" PVC                         HOME DEPOT    l0 FT        $4

                                                                                                    MATERIAL ESTIMATE @ $240

Down load manual for Macerator pump