....and if you're looking for a rust remover, dazzlenation....lol...as far as i can remember - the plumber that had 'fixed' the stopcock...."a bit of this will get it working in no time" etc etc....had used the following product with a 'smart straw'....go figure:

WD-40 44410 Multi-Use Product Smart Straw 300ml : Amazon.co.uk: Business, Industry & Science

Dazzlenation (tumblr.com)

https://64.media.tumblr.com/ee1e0c15f5c9e55ac7ce5cf6fcc8303c/10398e66fae3e684-b2/s500x750/e63d38e655367a69b12e66e5ee7bff8f41190548.gifv