We have recently bought a 22 year old nb with a Sealand Traveller drop through loo. Everything has been working fine but we are getting a strange kind of sweet smell appearing in various cupboards around the boat. We are fairly sure the holding tank is not leaking as the bilges are completely dry. However, we are wondering if it could be something to do with the vent, which at the moment we haven't been able to locate.....?! So our question is, should there be a vent and if so could this be the source of this strange smell working its way through the bilges and up in to the cupboards? Thanks