Thanks, that is very helpful. I usually fill up from a dockside refuelling point so had envisaged putting the filter funnel into the tank filler hole (which is horizontal on the 36 Classic) and then pouring the fuel into the funnel from the dockside fuel pump. The size of the filter is 50 microns and is the same for all the funnels but because the fuel comes out of the pump at quite a fast rate I think I would need a fairly large capacity funnel. The 19 litre per minute would probably just be about ok. I thought I could steady the funnel with one hand and operate the pump with the other.
The question is whether it is worth the cost of the filter funnel which for the 19 LPM would be about £85. The quality of fuel on the south coast is on the whole pretty good but it only takes one batch of contaminated fuel to cause problems.