This is what I used on my last one, had two of them so could switch between tanks & both off as an anti-theft. Didn't pay as much as these are though only about £8. But I did email the guy I got mine from a couple of months ago & never got a reply. If we can get the price down to £10 each I'll have two.
Another fudging edit:- Just found the invoice I paid £7.50 plus delivery for them, he was going to do a deal on 10 for £6.50. This is the same guy as well, maybe his email has changed.