A possible repair:
If the flex hose is too short, and if you can get at it somewhere in the middle of the length of hose (perhaps right under the sink?), you can extend the hose by splicing in a length of plastic pipe as follows:
1 1/4" plastic drain plumbing (for under the sink as part of a J-trap assembly for a bathroom sink) is thin-walled pipe that fits the 1 1/4" flex hose nicely. It helps to use a file or fine sandpaper on the pipe to "taper" the cut so it slides into the hose...it's a snug fit.
Get a suitable length of pipe (perhaps a drain kit or a drain extender) and three stainless hose clamps.
Cut the flex hose where it's easy to manipulate it and where it runs straight for about a foot or so.
Insert a length of the plastic drain pipe in the hose to lengthen the hose....maybe you only need 2" or so of additional length, but you can insert 6" to 8" of pipe into the hose and simply slide the hose onto the pipe far enough to get the length you need. This allows adjustment as needed.
A simple hacksaw will cut this pipe easily, and you can cut the hose with a carpenter's knife. (My hose did not have a steel coil wire to reinforce it, but if yours is reinforced with wire, use a wire cuter [dikes] to get a clean cut on the wire after you cut the rest of the hose.)
Use two of the hose clamps to secure the hose to the pipe slice....but leave them loose until you make the connection to your drain plumbing.
Attach the end of the hose to your drain fitting and use the third hose clamp to secure it.
Adjust the length of the splice to be a comfortable fit and tighten the hose clamps on the plastic pipe.
Expect the flex hose to "shorten" up once you cut it. If the hose was "stretched" when installed, it will naturally return to its relaxed, shorter length. This is why the splice pipe should be longer than you expect to need.
I suspect that the person who assembled your drains cut the hose a bit too short and simply stretched it to make the connection. Or, maybe s/he was at the end of a reel of hose and needed 48" but only had 46"...and just made do. Whatever the cause, I've had to repair similar hose feeding my fresh tank. (It was penetrated by a screw through the floor and the fresh tank would slowly drain itself through the hole in top of my fill tube.) When I cut the hose to insert the "drain pipe splice", the hose immediately shortened up by about 2" or so. My splice has at least 2" of plastic pipe showing where the hose had once been continuous.
If this repair works for you, you might want to secure the section of the hose with the stiff pipe in it so that it can't get jammed up as you move the slide. They make zip ties with a screw hole that will work nicely to secure the pipe in a safe position:
https://smile.amazon.com/Install-Bay...ith+screw+hole"
IMPORTANT NOTE: Expect that your hose may be restrained with one or more of these from the factory, and you may need to cut and replace them in order to maneuver the hose as you need to. You might wiggle the hose through them, but probably not.
This repair may or may not work for you, but if it does, it may be easier than buying a new length of flex hose and replacing what you have with one that's long enough. If you can't access the middle of the hose or you can't find a place to insert the length of stiff pipe an hose clamps so that it won't get hung up when operating the slide, replace the drain hose with something that's actually long enough. Something like this should fit.
https://www.etrailer.com/RV-Plumbing.../CAM36601.html
I've used Fernco fittings. They are soft rubber. They need something solid to clamp to. To use a Fernco, you'd need a hard plastic pipe splice anyway, which brings us back to the splice recommended above.
Fernco 1-1/4 in. x 1-1/4 in. Flexible PVC Coupling-P1056-125 - The Home Depot Fernco may make a fitting with a hard plastic male 1 1/4" fitting that takes a hose and hose clamp on one end and a soft rubber 1 1/4" female on the other, but I have never seen one.
Good luck.
P.S. While you're in there, if you do much traveling over a rough road...say washboard gravel...snug up all those plumbing connections, then use Gorilla tape to secure them from vibrating loose. That conventional plumbing was designed for home use, and those connectors are notorious for coming apart from vibration.
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