Thetford Porta Potti 335 Portable ToiletThetford Porta Potti 335 Portable Toilet The Porta Potti 335 is the smallest flushable chemical toilet in the Thetford range, so it is very compact, and is suitable for VW campervans and boats where space is at a premium. The Porta Potti 335 with the Hold Down Kit (optional extra) which is perfect to use on boats! The toilet can be adapted with a special hold down kit to attach the toilet to the floor of your boat, wherever you want. The Hold Down Kit