It's all down to the old BBC Nationwide programme in my case. Those of a certain age will remember the nasal Yorkshire tones of Michael Barrett accompanied by Bob Wellings forever losing his script and looking at the wrong camera. Anyway, it was this programme that lives on within the industry (BBC in particular) with the phrase describing a filler insert as a 'skateboarding duck'. (It was in fact Nationwide that featured that very subject one day.)
Anyway ... there must have been some sort of forerunner of Bill's Splosh organisation as I remember in the mid-70s a feature on the UK final of the custard pie throwing contest. There they were out in a field somewhere with a load of couples standing a fixed distance apart. When the whistle blew, the pies flew and the couple most covered won.
Nearest the camera were a youngish couple. After a minute or so, they were both completely covered and the bloke, realising that there was nowhere else for him to cover, calmly walked up to the girl, lifted her skirt to reveal a very sexy body beneath in delightfully clinging tights and then splat - right between her legs! I suddenly realised that I found this remarkably interesting!

I would be about 11 or 12 I suppose. I didn't quite understand what was going on there but noted the huge grin and slightly glazed expression in the girl's eyes as the guy continued to massage it around there for quite a while. (This was on BBC1 at teatime, you understand! I think the significance had slipped past the director!)
So it was that I started a life-long passion for both sploshing and tights. I think it was the realisation that something so smooth, silky, yet tight and stretchy could almost but not quite hide that lovely shape underneath that got me started there. When I later realised that they were also ideal for holding lots of gloop as well, that was a revelation and I was hooked!