We have the Splendide washer/dryer in our 2005 Fleetwood 39S Excursion.
The first time we winterized it in Alaska we used pink RV antifreeze. We put it in the fresh water tank and pumped it into the WD by cycling like we were doing a load of wash.
Under the front of the cabinet where the WD is mounted there is about a 7" square wooden access cover than can be removed with four screws. With a flashlight we could see the pink antifreeze in all three lines.
I'm not sure why there are three clear plastic 1/2" lines to the WD. There would be the hot, cold and ??? Maybe the third one is the drain line so that it's flexible to take care of the WD vibrating?
Also on the bottom front of the WD is a round cover (2.5" dia?) that is the lint trap. It should be opened to drain water out of it and clean the lint out. This usually takes two people. The lint trap is under / behind the cover at the bottom of the WD. It takes one person to tilt the unit slightly backwards so the cover clears the wooden frame and a second person to unscrew the cover. Then we poured about a quart of antifreeze inside the WD and cycled it to get it through the drain.
So, if they winterized with pink antifreeze you should be able to see it in the clear hoses via the access door. If the winterized using air, there's nothing that you can really check.
This year when we winterized, we used air, besides pouring antifreeze down all of the drains, I also poured some in the bottom of the WD and cycled it.
You also face the same question about winterizing the ice cube maker in the freezer. If they used pink stuff you should be able to see, if they used air, you won't really be able to tell.
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.