Wash basin conundrum - help please??

Hi - we have just dipped out toes back into the world of caravans following a 20-year break and are finding the fixtures and fittings all much more complicate and trickier to fix than we remember, so are hoping than someone can help please.

We have a 2006 Lunar Ultima which has a vanity unit in the washroom encompassing a flip-up basin.  Unfortunately the waste pipe has come away from the basin, which caused a fairly serious flood before the damage was discovered, due to the water running down the back of the vanity unit/cassette loo, then pooling under the shower tray (why the flippin' heck is there carpet under the shower tray.... .).

Anyway, we have pulled everything apart and dried it all out - but I can't find a way to re-attach the waste hose to the basin, as the basin, which consists of a top and bottom,  appears to have been glued together after the waste pipe was attached, leaving only a small apeture at the side for the pipe to fit through, but not big enough to fit my hand.  I have tried to prise the two halves of the basin apart but this is going to break it, so do I have to buy a new one or will this arrive already glued together also?  It is very annoying as the basin is completely undamaged, I just can't reach in to re-attach the pipe?

I am sure one of you will have come across something similar before, and would be grateful for any advice?

Thanks in advance.