I ran power to the macerator via an 8 gauge cable a couple of months ago.
Do not skimp on the diameter of the power cable. Carefully measure the length of the proposed line route, add a couple of feet, and find the proper gauge on one of several 12 volt
voltage loss calculators on the web. Use the full 20 amp draw for the calculation. Be sure to properly fuse the power cable at the battery tie in point.
I tied in to the power at the battery, ran the cable externally under the belly wrap, and came up to the storage compartment closest to the sewer dump by drilling a hole through the floor and down through the belly pan.
I will be back to the trailer in a couple of days and will shoot some pics.
To me, using the 1 1/2" power macerator hose is MUCH easier than wrestling a 3" gravity drain hose. Cleanup is much easier also.