From the vendor website:
Do I need to buy a new/refill cylinder to return empty gas cylinders?
Absolutely not! We will happily organise for your cylinders to be collected free of charge!What if I don’t have an account with GasDeal?
You must have an account with GasDeal in order for us to assign you the
credit but don’t worry it only takes 2 minutes! You will be asked to
create an account after you submit your collection request.
Alternatively you can register a new account nowWhat if I don’t want or need any more gas cylinders and I just have empties for collection?
That’s fine, you will be asked to create an account with GasDeal so that
we can first attribute your credit on a successful collection of your
gas cylinder returns. Once you have the credit in your account you can
request a cheque or bank transfer of the credit value. Simply request
this in writing to email@example.com
TERMS & CONDITIONS
ONLY Flogas cylinders are allegeable [sic] for a refund.
In order to receive the refund the cylinder MUST be in a reusable
condition – this is determined by our supplier. If the supplier deems
that the condition of the cylinder is beyond reuse we will be unable to
apply the return fee, nor will we return the empty cylinder.
By requesting collection of a Flogas empty cylinder you are agreeing to the stated terms and conditions.