A ball valve won't do anything for you, a check valve or one way valve will though.
I assume these are returns from an open sump type setup? If they're returns from a canister filter you have nothing to worry about anyway as overflowing would be impossible.
For the sump the best siphon break is a simple hole *just* below the desired waterline, that way it doesn't spray water during normal use, but only allows a minimal amount to flow out in the event of an outage, just be sure the hole stays clean - as in not clogged.
I assume these are returns from an open sump type setup? If they're returns from a canister filter you have nothing to worry about anyway as overflowing would be impossible.
For the sump the best siphon break is a simple hole *just* below the desired waterline, that way it doesn't spray water during normal use, but only allows a minimal amount to flow out in the event of an outage, just be sure the hole stays clean - as in not clogged.