how to keep bubble-disk from floating?

I bought this bubble-disk (Penn-Plax 3" small Deluxe Bubble-Disk)
which has no suction cup or any way of adhering to the side/bottom of
my tank. It is lighter than water so floats naturally, which is
annoying.

The only thing I thought of was to rubber-band a rock to the back.
That helps somewhat but even that rock isn't really heavy enough--it
still wants to float up.

Advice, anyone? :-) (and also how to prevent tubing from being pinched
by lid, and secure it to the inside of the tank)

Thanks!
Jason

Jason in Oakland wrote in message
. ..
I bought this bubble-disk (Penn-Plax 3" small Deluxe Bubble-Disk)
which has no suction cup or any way of adhering to the side/bottom of
my tank. It is lighter than water so floats naturally, which is
annoying.

The only thing I thought of was to rubber-band a rock to the back.
That helps somewhat but even that rock isn't really heavy enough--it
still wants to float up.

Advice, anyone? :-) (and also how to prevent tubing from being pinched
by lid, and secure it to the inside of the tank)

Thanks!
Jason

get a bigger rock.