Just looking at IST Silicone Soft Flex Tube Snorkel....How does the mask clip work does it hook in from the top or bottom?
IST Snorkel Holder For IST SN60 Snorkel
The button with down arrow on it is part of the piece that sits on the mask strap. It slides into the snorkel-side clip from the bottom, i.e. the snorkel sits on top.
(They sell replacement mouth pieces and purge valves as well though it takes some googling to find a reseller.)