Attaching a photo of the pillar candle holder I have been using. I clip the horizontal plastic, and leave the vertical plastic pieces, which act as prongs to hold the oasis. This fits a half block of oasis.
Clip the plastic first, then apply cling or oasis clay to bottom to secure to top of eiffel tower. I have been using the tall eiffels (36 inch, I think, and also use a 8 inch mirror base fastened with clay to the bottom of the tower. Probably not necessary, but so far this has been working for me.)
Then add your wet oasis foam block, and secure with 2 pieces of waterproof tape, one horizontal, one vertical.
The clay does not stick as well if it gets wet, so I like to secure it to the vase first.
Victoria, what is an O-ring?