If yours is a ribbed fill hose, I'll make a recommendation. Do not replace it with the same ribbed hose. And here is why. The fresh water tank is made from polyethylene. This is needed to get a potable water tank and be food grade. It is one slippery plastic.
The problem with the ribbed hose is the ID of it. It is often not a nice smooth bore, it has depressions in it where the ribs are on the out side. And then to get the worm drive clamps to try and compress a seal nice and even is very difficult to close to impossible as the clamp pressure is on a rib and wants to slide off the rib as you tighten the clamp.
Sunline use to squirt clear silicone on the tank pipe (at least on mine they did) and then slip the ribbed hose over it. The silicone being so slippery against polyethylene, the hose will back off even with 2 worm drive clamps on it.
I tried many times to get mine to stop leaking and it was a challenge. I later found many have switched to the potable water clear vinyl hose which has a smooth bore and will seal very effectively against the fresh tank pipe. The tank pipe is also a smooth OD, there are no barbs. Using the potable water clear vinyl hose with no silicone and then using worm drive clamps has been reported to work from the get go.
I'm not saying the ribbed hose will not work. Most RV manufactures use it, the only reason I can think of why is lower cost and that it is harder to create a kink in it. Look at your hose you have now and the hose you are going to buy. If the ribbed hose has bumpy ID, the depressions are where the ribs are on the outside, be prepared for potential sealing issues. If they actually changed the hose to being a true smooth bore, no depression at all, then your odds will be higher of a seal. What Sunline used in the 2004 model year has the problem.
If you do go the potable water clear vinyl hose route, make sure you do not kink it. That is something to work through with it as it has no outer ribs. It may also be very stiff. You may have to soak it in hot water to possibly get it to flex easier. This potable water clear vinyl hose looks just like the vent hose for the fresh tank, just bigger in diameter. Home Depot and Lowes may carry it. I have seen it there, just do not know if they have that size.
PS, This "might" be the size. You will need to verify
Sioux Chief 1-5/8 in. O.D. x 1-1/4 in. I.D. x 2 ft. Clear Vinyl Tubing-HSVSP2 - The Home Depot
Shop Samar 1-5/8-in x 1-ft PVC Clear Vinyl Tubing at Lowes.com
The also sell the reinforced hose which may not kink as much. Do not know if they have it in the size needed
Shop Samar 1-in x 1-ft Reinforced PVC Reinforced Braided Vinyl Tubing at Lowes.com
They often sell it on a roll and you cut off what you need. That link may only by the foot long. Your looking for a smooth bore hose, is made from FDA rated material for potable water service. It does not have to the the clear vinyl, but need to be smooth bore and potable water rated.
Good luck and let us know how you make out.
Hope this helps
Current Sunlines: 2004 T310SR, 2004 T1950, 2004 T2475, 2007 T2499, 2004 T317SR
Prior Sunlines: 2004 T2499 - Fern Blue
2005 Ford F350 Lariat, 6.8L V10 W/ 4.10 rear axle, CC, Short Bed, SRW. Reese HP trunnion bar hitch W/ HP DC
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