I'll go all out and shave it, see if that helps any. The toggle switch is indeed set in the middle of that rotary valve to also seal/unseal it, but it's very very small and very very stiff - I wonder if even *too* stiff on mine. If I had three hands to operate both on and off whilst holding it upside down, not letting any air in, full of water and then upend and straddle it then sort the valves I'd be alright with it, but as it stands I'd say the majority of the time air gets in, seal isn't right somehow.
Whilst we're on the subject, once I have this down, have you ever had to replace any seals on yours? Have to replaced the base ever even? How long have you had it/do you still use it? If it's alright to ask all that!
Thanks CD.