Regarding overflow syphon similar to the readily available overflow boxes are awfully easy and cheap to DIY.
🙂
The acrylic boxes available in the trade, usually Made in the USA are pretty pricy inclusive of P&P up to a £ 100 and +
They all work following the principle of communicating vessels and gravity... You can make them from accordingly sized PVC pipe and fittings. Depending on how you like the flow pattern in the tank you can place a few in a smaller size than just one big chunky fellow.
2 x PVC T
1 x filter basket
1 x PVC Knee
1 X PVC Socket
2 x PVC Cap
2 x Reducer or rubber Union seal.
1 x U pipe made from tube and 2 knees.
It's the U pipe that makes the flow trough capacity, I made a few of these with 16 mm U pipe and it fits in 25mm T with a 16x25 reducer. The U pipe can be made in any size 19mm, 25mm whatever suits you best. Take a T size 1 x sized bigger thus if U is 25 take a 32 T (Or 40).
You need t sand out the inner bumper from the reducer so the U pipe can go all the way through with a snug fit. Don't glue it so it can be adjusted and taken out for cleaning.
Since the T's bottom ends are capped there will always be a water puddle in them when the U pipe is vacuumed it's will be a water lock and the U pipe stays filled and always autostart when water starts flowing.
The entire overflow can be taken out since the socket on the pipe to the sump isn't glued. Then take the complete assembled overflow and dip it underwater in the tank, turn it around a few times to get all air out then it will be completely filled with water and ready to run. Lift it out gently, keep it level to keep the water in, hang it over the glass panel stick it into the socket from the pipe to the sump.
🙂 As soon as the filter basket is below the water level in the tank it will start to syphon. You decide how deep you put it below the desired water level. Depending on the length of the U pipe legs it can be adjusted a little.
This is exactly the same as any other £100 overflow box, no difference. If the pump stops the water stop running when it gets below the basket, the water lock keeps it vacuumed and it will restart syphoning when the pump starts again.
This is the one I made from 16mm U pipe and 25mm T... I made 2 each back corner has 1...
Sorry for the algae it needs a clean...
😳
Always running, already for years and years to come... Never any issues... Forgot the cost... A few bucks no more...