My wife has on occasion blocked the sink in ours. The best way I have found to clear it is to find a place where you have access to mains pressure water, turn your hose with nozzle on narrow spray (highest pressure), put it to the drain in the sink, seal around it (clamp with hands should be enough), & have your wife turn the water on. The pressure should blow clear whatever blockage you have. Has always worked for me.

Regards Terry

thanks for your reply, but I have already tried the mains pressure and also from underneath having dropped the major hose connections off, to no avail but with water escaping throughout the rear floor area., I have come to the conclusion that the drainpipe is kinked somewhere behind the tap plumbing After using the hinged sink quite frequently without a problem, it is now completely blocked and will only drain by 'pumping' the sink up and down making me think that the hose is kinking when dropping the sink into a user position, there is a drain overflow behind the folded sink and I am estimating that the two drain areas have a joiner, if this is so that is approx where the blockage occurs, so I will need to take the whole tap plumbing system out to get access to the pipes, hence my request on getting the old sealant completely clean and enabling a good seal on replacement, thanks once again.