Is it possible you can get a bit of the same hose and twist or screw round & round til inside enough to hold position then one end into the van end & the other into the hanging down pipe. It you can you then wrap around with the waterproof duck tape to hold them together.
Might help as a temporary or even permanent job done.
If your onsite it is surprising how many might have a little bit of that hosing, ask around. We have at home & in stored c.van just incase, is was a cut off bit from the main pipe which was far too long.
It shouldn't be hard to replace the whole length of hose
from where it starts inside & along to the back. Plastic
becomes brittle with age which is probably why it broke.
Take a bit to a caravan dealer and get a pipe which will screw into the one you have or, bigger so it fits on the outside/..ive did this and just used plastic glue so it wont come back out.
Just a daft question...you say its an inch ?
Do you mean 1 inch outside diameter or 1 inch inside diameter ?
The one on the right if im right is for the shower stick it in a separate waste water barrel.
The one on the left and the middle can be joined by a 25mm "T"piece just get a piece of extra hose..
Hi Ratmanuk have a look at this site on how to upgrade your waste water pipes I changed mine last year, one of the best up grades on an older van ( no clogged up pipes with peas/carrots etc)