Has it always been like that or has it just developed the habit? If the waste pipe is clear with no blockages then I suspect it may be down to gravity - or lack of it - i.e. not enough "fall" from the bottom of the sink to the waste water container, or a hump in the hose somewhere. Does the hose go up before it goes down to the container? If so then move the container further away so it doesn't.
------------- Caz
If you can't see the light at the end of the tunnel, just keep going till you go round the bend.
I had to re-do my van when I got it, the kitchen sink took nearly 15mins to drain, looked underneath, and the hose went from the sink, fastened to the floor, under the floor beam, back up to the floor, before going to the outlet.
make sure the pipe only goes into the waste container about 2 inch no more,if the pipe is in the water it will not drain fast.try a bit of mr muscle drain cleaner.
------------- the only silly question is the one you do not ask.
Last time my Avondale was in for service, I asked the chaps to replace the kitchen drain hose for this very reason. The 'fall' looks OK with the new pipe, but it doesn't drain any quicker!
The most effective solution must be to replace all the flexible with rigid-tube plastic piping. I think I've seen articles about this but can't recall where.
It could be just down to a kink in the pipe somewhere or the pipe may have come unfastened under the van causing it to sag.
When had a 2 berth compass with a blocked drain once and I had the bright idea of back blowing it from outside with a airbed pump, caused a hell of a mess inside though no more probs with draining
I have a Bailey Pageant that has the same problem, pipes are very clear however did find that the right angle from the sink itself does restrict the flow a lot and I may well change it.
------------- Yesterday is history,tomorrow is a mystery and today is a gift,that's why they call it"the present"
Our pipes are at the back of the van and i always pitch with the back slightly down for this very reason. If we are dead level then it is alot slower. Never put fat or oil down the pipes and when you clean them out make sure you get stuff that is suitable for the plastic hoses as they are not as hardstanding as ones in your kitchen.
Had same problem on our new van, noticed the water was also staying in the plug hole so removed the sink (just the 4 screws and its out) to find the hose went uphill just after the plug hole so repositioned the pie so downhill only, problem solved. Also ripped all the waste pipes off the van and replumbed them from 2 rear outlets to 1 single side outlet using only a short run of pipework (discarded about 6-7metres of not needed pipe length) The bathroom waste even went fwd then inboard then all the way to the back of the van so any slight non level in any direction would have caused slow draining Who designs this stupid setup?
I had this problem with mine a while ago, I flushed it through, tried a plunger but nothing. I then purchased a bag of soda crystals and tried them down and you should have seen the sh*t that came out, god knows how many years crap had been lay in the pipes. So have a try with some I bought it from local pound shop.