Waste Water Hose

I had I think the same problem in March 2020, these are the answers I got which might be of some use to you
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You will some users took the chance to improve the system.
I ended up just getting the pipe from AS spares which was 1" or 26mm and forced it on to the 28mm tank fitting.

I remember thinking the setup was a collection from the parts bin with reducers to convert between imperial and metric fittings.  Each van could be different.
I know some people have an elbow on the tank end, some (like me) don't.  I think the elbow acts as a 28mm to 26mm reducer.

AS spares have it. They list it as 28mm which is standard caravan waste size, but its actually 26mm (1") and more flexible than the caravan stuff. You can get it in black from a garden centre that stocks aquatic stuff at £2 per metre but if you want grey (or blue for fresh water) then AS supply at £4 per metre plus £5 postage. So if you get from AS , get 2 metres so that way you'll have enough for the next time (and there will be a next time) and lowers cost of postage if you divide in 2.

Never heard of the company  before,  that pipe is exactly the same as AS supply, wish I'd known about it before. Their other stuff seems keenly priced as well.

When ours cracked (at about 2 years old) I fitted a section of rigid pvc pipe to the tank and crossed to the edge of the van terminating with a 90deg bend.  A short section of convoluted flexy is fitted to this so only the minimum amount of bending takes place.  The other advantage of the rigid pipe it stays away from the exhaust pipe.

try AS spares then.

try AS spares then.