As a contributor to a cycling forum, you could consider a Soudal sealant.
Sealant gun: you'll get an acceptable finish with whatever you can find.
PC Cox are a UK manufacturer of quality sealant guns.
Tajima make good sealant guns: https://www.dm-tools.co.uk/Tajima-Dual-Power-Sealant-resin-Gun/P17354
Mapei tho
Agreed, Mapei for tile grouts and their range of waterproofing kits. Soudal are sealant specialists.
@NotThamesWater started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
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As a contributor to a cycling forum, you could consider a Soudal sealant.
Sealant gun: you'll get an acceptable finish with whatever you can find.
PC Cox are a UK manufacturer of quality sealant guns.
Tajima make good sealant guns:
https://www.dm-tools.co.uk/Tajima-Dual-Power-Sealant-resin-Gun/P17354