It was somewhere outside Barstow when "Dee"
wrote:

You say silicone - not sealant?

Silicone is what it's made out of, sealant is what it does. Not all
sealants are silicones.

For aquaria, you want a silicone that's happy when submerged long-term
and doesn't leach out toxic nastiness. For a snake terrarium it's not
so important.

Costs around £3-5.

Cheaper if you don't buy from a shed - try Screwfix, or several others
(about £2).