Hi Catherine, we had our last van for just over 6 years and to prevent the smelly pipes I used to pour a little Zoflora down each plug hole after every outing. Also a couple of times a year we would push a trimmed cork into the outlet pipes outside the van and then pour Milton into the sinks leaving it in the sink (so that the pipes are filled with Milton) After half an hour or so pull the corks out to drain the Milton-voila!! lovely fresh pipes and sinksDon't put bleach down - it isn't like a plastic wastepipe at home! We bought some liquid specifically for the job, and use it when we get back home. Put an old rag up the opening of the outlet pipes, pour the liquid down the plughole, and it slowly seeps out leaving everything smelling fresh ready for the next trip. It's available from any caravan dealer - and it works!
http://www.fenwicks.net/fendox.htm[/quoteII use Fendox from Fenwicks and also put the pressure washer drain cleaner through
Grade do a water trap for caravan pipes as well
]http://www.fenwicks.net/fendox.htm