Since the shift from Goretex, not having a need for so much Techwash, iv'e been sourcing 5L at a time/ as needed, from Millets: https://www.millets.co.uk/
Thought their store may be worth sharing. No affiliation, kickbacks or trade discounts they just have great customer service, reasonable shipping and some good prices for the more 'entry level' of solid brands (currently have one of their berghaus tents for a squizz).